ASME B18.2.3.

3M-2007
[Revision of ANSI B18.2.3.3M-1979 (R2001)]

Metric Heavy
Hex Screws
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A N A M E R I C A N N AT I O N A L STA N DA R D

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 ASME B18.2.3.3M-2007
[Revision of ANSI B18.2.3.3M-1979 (R2001)]

Metric Heavy
Hex Screws

A N A M E R I C A N N AT I O N A L S TA N D A R D
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 Date of Issuance: October 31, 2007

This Standard will be revised when the Society approves the issuance of a new edition. There will
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Copyright © 2007 by
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 CONTENTS

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
Committee Roster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Correspondence With the B18 Committee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
1 Introductory Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 General Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Figures
1 Fillet Detail for Short Screws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Fillet Detail for Long Screws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Tables
1 Tolerance Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Dimensions of Heavy Hex Screws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3 Dimensions of Underhead Fillets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4 Length Tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5 Dimensions of Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6 Maximum Grip Gaging Lengths and Minimum Body Lengths . . . . . . . . . . . . . . . . . . . . . 5
7 Thread Lengths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Nonmandatory Appendices
A Screw Straightness Gage and Gaging Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

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B Body Position Gages and Gaging Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

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 FOREWORD

American National Standards Committee B18 for the standardization of bolts, screws, nuts,
rivets, and similar fasteners was organized in March 1922 as Sectional Committee B18 under
the aegis of the American Engineering Standards Committee (later the American Standards
Association, then the United States of America Standards Institute and, as of October 6, 1969,
the American National Standards Institute, Inc.) with the Society of Automotive Engineers and
the American Society of Mechanical Engineers as joint sponsors. Subcommittee 2 was subsequently
established and charged with the responsibility for technical content of standards covering wrench
head bolts and nuts.
At its meeting on December 4, 1974, Committee B18 authorized preparation of a series of
standards for metric fasteners. Subcommittee 2 was assigned responsibility for developing stan-
dards for metric hex bolts, screws, and nuts.
At a meeting on September 22, 1976, Subcommittee 2 organized the contents of a standard
covering eight different hex head screw and bolt products. Actual drafting was postponed until
ISO/TC2 could reach final decisions relating to basic dimensions and characteristics of hex bolts,
screws, and nuts. At ISO/TC2 meetings held in April 1977, final actions were taken. Committee B18
affirmed the TC2 decisions at a meeting on June 29, 1977, and drafting of this Standard was
started.
In February 1978, Committee B18 established a cooperative program with the Department of
Defense to draft American National Standards for metric fasteners in such a way that they could
be used directly by the Government for procurement purposes. The Department of Defense
requested that each of the eight products be covered in separate standards, and Subcommittee 2
accepted this approach at its meeting on June 27, 1978.
The 1979 Edition was approved by ballot of Committee B18 on September 15, 1978, and was
subsequently approved by the secretariat and submitted to the American National Standards
Institute for designation as an American National Standard. This was granted on March 26, 1979.
This revision was approved by the American National Standards Institute (ANSI) on
July 11, 2007.

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 ASME B18 COMMITTEE
Standardization of Bolts, Nuts, Rivets, Screws,
Washers, and Similar Fasteners
(The following is the roster of the Committee at the time of approval of this Standard.)

STANDARDS COMMITTEE OFFICERS

D. A. Clever, Chair
R. D. Strong, Vice Chair
S. W. Vass, Vice Chair
R. L. Crane, Secretary

STANDARDS COMMITTEE PERSONNEL

V. Cartina, Aztech Locknut J. F. Koehl, Corresponding Member, Spirol International Corp.
D. A. Clever, Deere & Co. W. H. Kopke, ITW Shakeproof Assembly Components
A. P. Cockman, Ford Motor Co. J. G. Langenstein, Member Emeritus, Consultant
R. L. Crane, The American Society of Mechanical Engineers W. J. Lutkus, Heli-Coil Emhart
A. C. DiCola, Wrought Washer Co. D. A. McCrindle, Canadian Fasteners Institute
B. A. Dusina, Federal Screw Works M. D. Prasad, Corresponding Member, General Motors Corp.
J. S. Foote, Corresponding Member, Trade Association W. L. Sakowski, Account Managers, LLC
Management, Inc. S. Savoji, ITW Medalist
D. S. George, Ford Motor Co. W. R. Schevey, Corresponding Member, BGM Fastener Co., Inc.
J. Greenslade, Corresponding Member, Greenslade and Co. W. R. Stevens, Ramco
J. J. Grey, Corresponding Member, Fastener Consulting Services, R. D. Strong, General Motors Corp.
Inc. S. W. Vass, Consultant
B. Hasiuk, Corresponding Member, Defense Industrial Supply C. B. Wackrow, MNP Corp.
Center Philadelphia W. K. Wilcox, Consultant
A. Herskovitz, Consultant C. B. Williamson, Fastenal Co.
J. Hubbard, Corresponding Member, Rockford Fastener, Inc. C. J. Wilson, Industrial Fasteners Institute
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J. Jennings, Corresponding Member, Naval Surface Warfare Center R. B. Wright, Corresponding Member, Wright Tool Co.
M. Keller, Corresponding Member, Paracad Technology Co. J. G. Zeratsky, National Rivet and Manufacturing Co.

SUBCOMMITTEE 2 — EXTERNALLY DRIVEN FASTENERS

S. W. Vass, Chair, Consultant J. Hubbard, Rockford Fastener, Inc.
C. B. Williamson, Vice Chair, Fastenal Co. J. Jennings, Corresponding Member, Naval Surface Warfare Center
R. L. Crane, Secretary, The American Society of Mechanical M. Keller, Paracad Technology Co.
Engineers W. H. King, Porteous Fastener Co.
D. A. Clever, Deere & Co. D. McCrindle, Canadian Fasteners Institute
A. P. Cockman, Ford Motor Co. R. B. Meade, R. Bruce Meade & Associates, LLC
P. J. DeChant, Barnes Distribution S. Savoji, ITW Medalist
C. A. Dugal, TSP G. M. Simpson, Semblex Corp.
B. A. Dusina, Federal Screw Works Q. M. Smith III, Dana Corp.
J. S. Foote, Trade Association Management, Inc. W. R. Stevens, Ramco
D. S. George, Ford Motor Co. R. D. Strong, General Motors Corp.
J. Greenslade, Greenslade & Co. C. B. Wackrow, MNP Corp.
A. Herskovitz, Consultant W. K. Wilcox, Consultant
M. W. Holubecki, Electric Boat Corp. C. J. Wilson, Industrial Fasteners Institute

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 CORRESPONDENCE WITH THE B18 COMMITTEE

General. ASME Standards are developed and maintained with the intent to represent the
consensus of concerned interests. As such, users of this Standard may interact with the Committee
by requesting interpretations, proposing revisions, and attending Committee meetings. Corre-
spondence should be addressed to:
Secretary, B18 Standards Committee
The American Society of Mechanical Engineers
Three Park Avenue
New York, NY 10016-5990

Proposing Revisions. Revisions are made periodically to the Standard to incorporate changes
that appear necessary or desirable, as demonstrated by the experience gained from the application
of the Standard. Approved revisions will be published periodically.
The Committee welcomes proposals for revisions to this Standard. Such proposals should be
as specific as possible, citing the paragraph number(s), the proposed wording, and a detailed
description of the reasons for the proposal, including any pertinent documentation.
Proposing a Case. Cases may be issued for the purpose of providing alternative rules when
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The request for an interpretation should be clear and unambiguous. It is further recommended
that the inquirer submit his/her request in the following format:

Subject: Cite the applicable paragraph number(s) and the topic of the inquiry.
Edition: Cite the applicable edition of the Standard for which the interpretation is
being requested.
Question: Phrase the question as a request for an interpretation of a specific requirement
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suitable for general understanding and use, not as a request for an approval
of a proprietary design or situation. The inquirer may also include any plans
or drawings, which are necessary to explain the question; however, they
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Requests that are not in this format may be rewritten in the appropriate format by the Committee
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ASME procedures provide for reconsideration of any interpretation when or if additional
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Attending Committee Meetings. The B18 Standards Committee regularly holds meetings, which
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 ASME B18.2.3.3M-2007

METRIC HEAVY HEX SCREWS

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1 INTRODUCTORY NOTES ASME B18.2.8, Clearance Holes for Bolts, Screws, and
Studs
1.1 Scope ASME B18.12, Glossary of Terms for Mechanical
1.1.1 This Standard covers the complete general Fasteners
and dimensional data for metric heavy hex screws recog- ASME B18.18.1, Inspection and Quality Assurance for
nized as American National Standard. General Purpose Fasteners
ASME B18.18.2, Inspection and Quality Assurance for
1.1.2 The inclusion of dimensional data in this High-Volume Machine Assembly Fasteners
Standard is not intended to imply that all of the sizes ASME B18.24, Part Identifying Number (PIN) Code
in conjunction with the various options described herein System Standard for B18 Fastener Products
are stock items. Consumers should consult with suppli- ASME Y14.5M, Dimensioning and Tolerancing
ers concerning lists of stock production sizes.
Publisher: The American Society of Mechanical
1.2 Comparison With ISO Standards Engineers (ASME), Three Park Avenue, New York,
NY 10016-5990; Order Department, 22 Law Drive,
1.2.1 ISO has not yet initiated development of an P.O. Box 2300, Fairfield, NJ 07007-2300
ISO standard for heavy hex screws. However, nominal
diameters and thread pitches, body diameters, widths ASTM F 468M, Specification for Nonferrous Bolts, Hex
across flats, bearing surface diameters, head heights, Cap Screws, and Studs for General Use (Metric)
thread lengths, thread dimensions, and nominal lengths ASTM F 568M, Specification for Carbon and Alloy Steel
are in accord with ISO standards for related hex head Externally Threaded Metric Fasteners
screws and bolts. ASTM F 738M, Specification for Stainless Steel Metric
Bolts, Screws, and Studs
1.2.2 Letter symbols designating dimensional ASTM F 1941M, Electrodeposited Coatings on Threaded
characteristics are in accord with those used in ISO stan- Fasteners (Metric)
dards, except capital letters have been used instead of
Publisher: ASTM International (ASTM), 100 Barr Harbor
the lowercase letters used in ISO standards.
Drive, West Conshohocken, PA 19428
1.3 Terminology
For definitions of terms relating to fasteners or compo- 2 GENERAL DATA
nent features thereof used in this Standard, refer to
2.1 Heads
ASME B18.12.
2.1.1 Top of Head. The top of head shall be full
1.4 Dimensions form and chamfered or rounded. The diameter of the
1.4.1 All dimensions in this Standard are in milli- chamfer circle or the start of rounding shall be equal to
meters, unless stated otherwise. the maximum width across flats within a tolerance of
−15%.
1.4.2 Symbols specifying geometric characteristics
are in accord with ASME Y14.5M. 2.1.2 Head Height. The head height is the distance,
as measured parallel to the axis of the screw, from the
1.5 Referenced Standards top of the head to the plane of the bearing surface.
The following is a list of publications referenced in this 2.1.3 Wrenching Height. The wrenching height is
Standard. Unless otherwise specified, the standard(s) the distance, measured at a corner of the hex, from the
referenced shall be the most recent issue at the time of plane of the bearing surface to the last plane of full
order placement. formed hex, i.e., the plane closest to the top of head at
which the width across corners of the hex is within its
ASME B1.3M, Screw Thread Gaging Systems for
specified limits.
Dimensional Acceptability — Inch and Metric Screw
Threads 2.1.4 Corner Fill. The rounding due to lack of fill at
ASME B1.13M, Metric Screw Threads — M Profile the six corners of the head shall be reasonably uniform.

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 ASME B18.2.3.3M-2007

2.1.5 True Position of Head. At maximum material Table 1 Tolerance Zone

condition, the axis of the hex head shall be located at true Nominal Head True Minimum Body
position with respect to the axis of the screw (determined Screw Position Diameter for
over a distance under the head equal to one screw diame- Diameter Tolerance Product Position
ter) within a tolerance zone of diameter specified in and Thread Zone Threaded of Body
Table 1. Pitch, D Diameter to Head, Dsi to Thread

2.1.6 Bearing Surface. The bearing surface shall be M12 ⴛ 1.75 0.84 10.68 0.70
flat and washer-faced. Diameter of bearing surface shall M14 ⴛ 2 0.98 12.50 0.70
not exceed the width across flats nor be less than the M16 ⴛ 2 1.12 14.50 0.70
specified minimum washer face diameter. For referee M20 ⴛ 2.5 1.40 18.16 0.84
purposes, measurement of bearing surface diameter M24 ⴛ 3 1.68 21.80 0.84
shall be taken at 0.1 mm above the bearing surface. The M30 ⴛ 3.5 2.10 27.46 0.84
plane of the bearing surface shall be perpendicular to M36 ⴛ 4 2.52 33.12 1.00
the axis of the body within the circular runout specified
in Table 2. The measurement of bearing face runout shall
be made as close to the periphery of the washer face as straightness tolerance diameter equal to 0.006L for nomi-
possible, while the screw is held in a collet or other nal screw lengths, L, 300 mm or shorter and 0.008L for
gripping device at a distance equal to one screw diame- screws having nominal lengths, L, over 300 mm through
ter from the underside of the head. 600 mm. A gage and gaging procedure to check
2.1.7 Underhead Fillet. The fillet configuration at straightness is given in Nonmandatory Appendix A.
the junction of the head and shank shall be as shown
2.6 Thread Length
in Figs. 1 and 2, and shall have limits as specified in
Table 3. The fillet shall be a smooth and continuous curve 2.6.1 The length of thread on screws shall be con-
fairing smoothly into the underhead bearing surface and trolled by the maximum grip gaging length, Lg, and the
the shank within the limits specified. No radius in the minimum body length, Ls, as set forth in paras. 2.6.2
fillet contour shall be less than R minimum. through 2.6.5.

2.2 Body Diameter 2.6.2 Grip gaging length, Lg maximum, is the dis-
tance measured parallel to the axis of the screw, from
The diameter of the body on screws that are not
the underhead bearing surface of the face of a noncoun-
threaded full length shall be within the limits specified
terbored or noncountersunk standard GO thread ring
in Table 2. For screws threaded full length, the diameter
gage assembled by hand as far as the thread will permit.
of the unthreaded shank under the head shall not exceed
For standard diameter-length combinations of screws,
the specified maximum body diameter, nor be less than
the values for Lg maximum are specified in Table 6. For
the minimum body diameter specified in Table 1.
diameter-length combinations not listed in Table 6, the
2.3 Screw Length maximum grip gaging length, as calculated and rounded
to one decimal place, shall be equal to the nominal screw
The length of the screw shall be measured parallel to
length, L, minus the reference thread length, B, as speci-
the axis of the screw from the underhead bearing surface
fied in Table 1 (Lg max. p L − B). Lg maximum shall be
to the extreme end of the shank. Tolerances for screw
used as a criterion for inspection.
lengths are given in Table 4.
2.6.3 Body length, Ls minimum, is the distance,
2.4 Points measured parallel to the axis of the screw, from the
The end of the screw shall be chamfered from a diame- underhead bearing surface to the last scratch of thread --`,```,`,,``,`,``````,,```,````-`-`,,`,,`,`,,`---

ter equal to or slightly less than the thread root diameter or top of the extrusion angle, whichever is closest to
to produce a length of chamfer or incomplete thread the head. For standard diameter–length combinations
within the limits for U specified in Table 5. The end of of screws, the values of Ls minimum are specified in
the screw shall be reasonably square with the axis of Table 6. For diameter–length combinations not listed in
the screw, and where pointed blanks are used, the slight Table 6, the minimum body length, as calculated and
rim or cup resulting from roll-threading shall be permis- rounded to one decimal place, shall be equal to the
sible. At the manufacturer’s option, the end of the screw maximum grip gaging length as computed minus the
may have a rounded point of radius, Re, as specified in reference transition thread length as specified in Table 7
Table 5. (Ls min. p Lg max. − X ref.). Ls minimum shall be used
as a criterion for inspection. Screws of nominal lengths
2.5 Straightness equal to or less than the length, Lu, as specified in Table 7
At maximum material condition, the axes of the screw shall be threaded full length. For screws that are
body and thread major diameter shall be within a threaded full length, the distance from the underhead

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 ASME B18.2.3.3M-2007

Table 2 Dimensions of Heavy Hex Screws

K L (See para. 2.3)
KW Lg (See para. 2.6.2)
Ls (See para. 2.6.3)
Para. 2.1.5 M A M S Fillet
(see para. 2.1.7) C (B) (See para. 2.6.4)
(X) (See para. 2.6.5)
Re
U

E Da DW Ds

Optional point
C construction
30°
Para. 2.5 M (see para. 2.4)
Property class and 15°
source identification Para. 2.7 M C M
to appear on top of head Para. 2.1.6 A
(see para. 2.10) A
Runout
Washer of
Nominal
Wrenching Face Bearing
Screw
Diameter Body Width Across Width Across Head Heights, Height, Washer Face Diameter, Surface
Diameter, DS Flats, S Corners, E K KW Thickness, C DW FIM
and Thread
Pitch Max. Min. Max. Min. Max. Min. Max. Min. Min. Max. Min. Min. Max.

M12 ⴛ 1.75 12.00 11.73 21.00 20.67 24.25 23.35 7.76 7.24 5.2 0.6 0.3 19.6 0.39
M14 ⴛ 2 14.00 13.73 24.00 23.67 27.71 26.75 9.09 8.51 6.2 0.6 0.3 22.5 0.43
M16 ⴛ 2 16.00 15.73 27.00 26.67 31.18 30.14 10.32 9.68 7.0 0.8 0.4 25.3 0.48

M20 ⴛ 2.5 20.00 19.67 34.00 33.00 39.26 37.29 12.88 12.12 8.8 0.8 0.4 31.4 0.59
M24 ⴛ 3 24.00 23.67 41.00 40.00 47.34 45.20 15.44 14.56 10.5 0.8 0.4 38.0 0.70
M30 ⴛ 3.5 30.00 29.67 50.00 49.00 57.74 55.37 19.48 17.92 13.1 0.8 0.4 46.6 0.85
M36 ⴛ 4 36.00 35.61 60.00 58.80 69.28 66.44 23.38 21.72 15.8 0.8 0.4 55.9 1.01

See para. 2.2 2.2 ... ... 2.1.3, 2.1.3, 2.10 2.10 2.1.3 2.1.6 2.1.6 2.1.6 2.1.6
2.1.4 2.1.4

Fig. 1 Fillet Detail for Short Screws Fig. 2 Fillet Detail for Long Screws
Fillet shall lie within Fillet shall lie within
this envelope this envelope
Dsi ,
Da1, min. Ds,
min. max. Da, max.
Da,
Da max. Da
Ds
Radius
R R
F1,
max.
F1 F,
max.
F

3
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 ASME B18.2.3.3M-2007

Table 3 Dimensions of Underhead Fillets

Fillet
Fillet Transition Diameter Radius
Fillet Length
For Short For Short
Nominal
For Short and Long For Long For Short and Long
Screw
Screws, Da1 Screws, Da Screws, F Screws, F1 Screws, R
Diameter and
Thread Pitch Min. Max. Max. Max. Min.

M12 ⴛ 1.75 12.2 13.7 3.0 1.3 0.6

M14 ⴛ 2 14.1 15.7 3.0 1.4 0.6
M16 ⴛ 2 16.5 17.7 3.0 1.6 0.6

M20 ⴛ 2.5 20.7 22.4 4.0 2.1 0.8

M24 ⴛ 3 24.5 26.4 4.0 2.3 0.8
M30 ⴛ 3.5 30.8 33.4 6.0 3.0 1.0
M36 ⴛ 4 36.6 39.4 6.0 3.1 1.0

GENERAL NOTES:
(a) Short screws are screws that are threaded full length.
(b) Values of Dsi are given in Table 1.

Table 4 Length Tolerances

Nominal Screw Diameter
Nominal Length M12 Through M16 M20 and M24 M30 and M36

To 10 mm ±0.3 ... ...

Over 10 mm to 18 mm ±0.4 ... ...
Over 18 mm to 30 mm ±0.4 ±0.7 ...

Over 30 mm to 50 mm ±0.8 ±1.3 ±1.5

Over 50 mm to 80 mm ±1.0 ±1.5 ±1.8
Over 80 mm to 120 mm ±1.1 ±1.8 ±2.0
Over 120 mm to 180 mm ±1.3 ±2.0 ±2.3
Over 180 mm to 240 mm ±2.3 ±2.3 ±3.0
Over 240 mm ±3.0 ±3.0 ±3.0

GENERAL NOTE: All tolerances are plus and minus.

Table 5 Dimensions of Points

Point Length, U
Nominal Screw Approx. Point
Diameter and Radius, Re [Notes (2), (3)]
Thread Pitch [Note (1)] Max. Min.

M12 ⴛ 1.75 16.8 3.50 0.88

M14 ⴛ 2 19.6 4.00 1.00
M16 ⴛ 2 22.4 4.00 1.00
M20 ⴛ 2.5 28.0 5.00 1.25
M24 ⴛ 3 33.6 6.00 1.50
M30 ⴛ 3.5 42.0 7.00 1.75
M36 ⴛ 4 50.4 8.00 2.00

NOTES:
(1) Re p 1.4 times thread major diameter
(2) U max. p 2.0 times thread pitch
(3) U min. p 0.5 times thread pitch

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 ASME B18.2.3.3M-2007

Table 6 Maximum Grip Gaging Lengths and Minimum Body Lengths

Nominal Diameter and Thread Pitch
M12 ⴛ 1.75 M14 ⴛ 2 M16 ⴛ 2 M20 ⴛ 2.5 M24 ⴛ 3 M30 ⴛ 3.5 M36 ⴛ 4
Nominal
Length, Lg Ls Lg Ls Lg Ls Lg Ls Lg Ls Lg Ls Lg Ls
L Max. Min. Max. Min. Max. Min. Max. Min. Max. Min. Max. Min. Max. Min.

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20 2.6 3.0
25 4.4 3.0 3.0
30 4.4 5.0 3.0 3.8
35 4.4 5.0 5.0 3.8 7.5
40 4.4 5.0 5.0 3.8 7.5 8.8
45 15.0 6.2 5.0 5.0 6.2 7.5 8.8 10.0
50 20.0 11.2 16.0 6.0 5.0 6.2 7.5 8.8 10.0
(55) 25.0 16.2 21.0 11.0 17.0 7.0 6.2 7.5 8.8 10.0
60 30.0 21.2 26.0 16.0 22.0 12.0 6.2 7.5 8.8 10.0
(65) 35.0 26.2 31.0 21.0 27.0 17.0 19.0 6.5 7.5 8.8 10.0
70 40.0 31.2 36.0 26.0 32.0 22.0 24.0 11.5 7.5 8.8 10.0
(75) 45.0 36.2 41.0 31.0 37.0 27.0 29.0 16.5 7.5 8.8 10.0
80 50.0 41.2 46.0 36.0 42.0 32.0 34.0 21.5 26.0 11.0 8.8 10.0
(85) 55.0 46.2 51.0 41.0 47.0 37.0 39.0 26.5 31.0 16.0 8.8 10.0
90 60.0 51.2 56.0 46.0 52.0 42.0 44.0 31.5 36.0 21.0 8.8 10.0
100 70.0 61.2 66.0 56.0 62.0 52.0 54.0 41.5 46.0 31.0 34.0 16.5 10.0
110 80.0 71.2 76.0 66.0 72.0 62.0 64.0 51.5 56.0 41.0 44.0 26.5 32.0 12.0
120 90.0 81.2 86.0 76.0 82.0 72.0 74.0 61.5 66.0 51.0 54.0 36.5 42.0 22.0
130 90.0 80.0 86.0 76.0 78.0 65.5 70.0 55.0 58.0 40.5 46.0 26.0
140 100.0 90.0 96.0 86.0 88.0 75.5 80.0 65.0 68.0 50.5 56.0 36.0
150 106.0 96.0 98.0 85.5 90.0 75.0 78.0 60.5 66.0 46.0
160 116.0 106.0 108.0 95.5 100.0 85.0 88.0 70.5 76.0 56.0
(170) 118.0 105.5 110.0 95.0 98.0 80.5 86.0 66.0
180 128.0 115.5 120.0 105.0 108.0 90.5 96.0 76.0
(190) 138.0 125.5 130.0 115.0 118.0 100.5 106.0 86.0
200 148.0 135.5 140.0 125.0 128.0 110.5 116.0 96.0
220 147.0 132.0 135.0 117.5 123.0 103.0
240 167.0 152.0 155.0 137.5 143.0 123.0
260 175.0 157.5 163.0 143.0
280 195.0 177.5 183.0 163.0
300 215.0 197.5 203.0 183.0

GENERAL NOTES:
(a) Lg is grip gaging length; Ls is body length.
(b) Diameter–length combinations between the dashed lines and the heavy solid lines are recommended. Lengths in parentheses are not
recommended.
(c) Screws with lengths above the heavy solid line are threaded full length.
(d) For screws with lengths longer than the lower dashed lines, Lg and Ls values shall be computed from equations as given in para. 2.6
of General Data.

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 ASME B18.2.3.3M-2007

Table 7 Thread Lengths

Thread Length, B, Ref. Transition Screws Threaded Full Length, Lu
Nominal
Screw Screw Screw Thread Screw
Diameter and Lengths Screw Lengths Lengths Length, X Screw Lengths
Lengths Maximum Maximum
Thread Pitch ≤125 >125 and <200 ≥200 Ref. to and Incl. Lg Over To and Incl. Lg

M12 ⴛ 1.75 30 36 49 8.8 24 2.6 24 40 4.4

M14 ⴛ 2 34 40 53 10.0 28 3.0 28 45 5.0
M16 ⴛ 2 38 44 57 10.0 32 3.0 32 50 5.0

M20 ⴛ 2.5 46 52 65 12.5 40 3.8 40 60 6.2

M24 ⴛ 3 54 60 73 15.0 ... ... ... 75 7.5
M30 ⴛ 3.5 66 72 85 17.5 ... ... ... 90 8.8
M36 ⴛ 4 78 84 97 20.0 ... ... ... 100 10.0

bearing surface to the face of a noncounterbored or non- (unplated or uncoated) screws, and to plated or coated
countersunk standard GO thread ring gage assembled screws before plating or coating. For plated or coated
by hand as far as the thread will permit shall not exceed screw threads, Class 6h tolerance high limit (GO) and
the length, Lg, as specified in Table 7. Class 6g tolerance low limit (NOT GO) shall apply.
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2.6.4 Thread length, B, as specified in Table 7 is a 2.8.2 Thread Gaging. Unless otherwise specified,
reference dimension intended for calculation purposes dimensional acceptability of screw threads shall be
only, and is the distance measured parallel to the axis based on System 21 of ASME B1.3M.
of the screw, from the extreme end of the screw to the
last complete (full form) thread. 2.9 Material and Mechanical Properties
2.9.1 Carbon and Alloy Steel. Materials and prop-
2.6.5 Transition thread length, X, as specified in
erty class shall conform to ASTM F 568M.
Table 7 is a reference dimension intended for calculation
purposes only. It includes the length of incomplete 2.9.2 Corrosion-Resistant Steels. Unless otherwise
threads and tolerances on grip gaging length and body specified, corrosion-resistant screws shall conform to the
length. The transition from full thread to incomplete requirements of ASTM F 738M.
thread shall be smooth and uniform. The major diameter
2.9.3 Nonferrous Metals. Unless otherwise speci-
of the incomplete threads shall not exceed the actual
fied, nonferrous screws shall conform to the require-
major diameter of the complete (full form) threads. For
ments of ASTM F 468M.
screws of property class 10.9 and higher strength materi-
als (tensile strength 1040 MPa and higher), the transition 2.10 Identification Symbols
threads shall have a rounded root contour, no radius of
Identification marking symbols shall be on top of the
which shall be less than the specified minimum radius
screw heads and shall be raised or indented at the manu-
at the root of the full-form thread.
facturer’s option, unless otherwise specified at the time
2.7 Position of Body-to-Thread of order. Markings shall be legible to the unaided eye
with the exception of corrective lens. Minimum height
For products with cut threads at maximum material of property class symbols shall be 3.2 mm for M12 and
condition, the axis of the screw body, Ds, over a length M14 screws, and 4.0 mm for M16 and larger screws.
equal to the nominal screw diameter from the last scratch When raised, markings shall project not less than 0.1 mm
of thread, shall be within the positional zone diameter for M12 and M14 screws, and 0.3 mm for M16 and larger
specified in Table 1, with respect to the axis of the thread, screws above the surface of the head. Total head height
over a length equal to the nominal screw diameter from (head plus markings) shall not exceed the specified max-
the last complete thread. A gage and gaging procedure imum head height plus 0.3 mm for M12 and M14 screws,
for checking body position is given in Nonmandatory and 0.4 mm for M16 and larger screws.
Appendix B.
2.10.1 Property Class Symbols. Each screw shall
2.8 Screw Threads be marked in accordance with the requirements of the
applicable specification for its chemical and mechanical
2.8.1 Thread Series and Tolerance Class. Threads
requirements.
shall be metric coarse thread series conforming to
dimensions for general purpose external threads given 2.10.2 Source Symbols. Each screw shall be marked
in ASME B1.13M, unless otherwise specified by the pur- to identify its source, manufacturer, or private label dis-
chaser. The Class 6g tolerance shall apply to plain finish tributor.

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 ASME B18.2.3.3M-2007

2.11 Finish If verifiable in-process inspection is used during man-

Unless otherwise specified, screws shall be supplied ufacturing, inspection sample sizes and reporting shall
with a natural (as processed) finish, unplated or be in accordance with the applicable ASME or ASTM
uncoated in a clean condition and lightly oiled. quality system consensus standard.

2.12 Workmanship 2.14.2 For nondesignated characteristics, the pro-

visions of ASME B18.18.1 shall apply.
Screws shall not contain an excess of surface imperfec-
tions that might affect their serviceability, such as burrs,
2.15 Clearance Holes
seams, laps, loose scale, and other irregularities.
The recommended sizes of clearance holes in material
2.13 Inspection and Quality Assurance to be assembled using heavy hex screws are the normal
Unless otherwise specified, acceptability of screws series given in Table 3 of ASME B18.2.8.
shall be determined in accordance with ASME B18.18.1.
2.16 Designation
2.14 Dimensional Conformance
Heavy hex screws shall be designated by the following
Products shall conform to the specified dimensions.
data, preferably in the sequence shown: product name,
2.14.1 Inspection of Designated Characteristics. identification of the standard, nominal diameter and
Unless otherwise specified, the following provisions thread pitch, nominal length, steel property class or
shall apply for inspection of dimensional characteristics. material identification, and protective coating, if
The designated characteristics are defined within the required.
following table and shall be inspected in accordance
with ASME B18.18.2 to the inspection level shown: NOTE: It is common practice in ISO standards to omit thread
pitch from the product size designation when screw threads are
Characteristic Inspection Level the metric coarse thread series, e.g., M20 is M20 ⴛ 2.5.

Thread acceptability C EXAMPLES:

Body diameter, Ds C (1) Heavy hex screw, ASME B18.2.3.3M, M36 ⴛ 4 ⴛ 180, Class
Head width across corners, E C 8.8; zinc plated, ASTM F 1941M, Fe/Zn 3C
Grip length, Lg max. C
(2) Heavy hex screw, ASME B18.2.3.3M, M16 ⴛ 2 ⴛ 80, silicon
Screw length, L C
bronze, ASTM F 468M Grade 651
Visual inspection [Note (1)] C
NOTE: 2.17 Part Identifying Number
(1) Visual inspection shall include property class, source marking,
fillet, and workmanship. For a part identifying number, refer to ASME B18.24.

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 ASME B18.2.3.3M-2007

NONMANDATORY APPENDIX A
SCREW STRAIGHTNESS
GAGE AND GAGING PROCEDURE

The conformance of screws to shank straightness or the rails equal to this distance by obtaining common
camber limitations set forth in para. 2.5 shall be checked readings on both micrometer heads. The movable rail
by using the gage illustrated in Fig. A-1 in accordance shall then be locked in place by tightening securing
with the following procedure. screws.
Allowable total camber on the product to be inspected The product shall then be inserted between rails and
shall be calculated in accordance with para. 2.5. The shall be rotated by hand through full 360 deg. Any
total camber thus derived shall be added to the specified interference occurring between the product and the gage
maximum body diameter, and the movable rail of gage that is sufficient to prevent rotation shall indicate exces-
shall be adjusted to provide a parallel space between sive camber.

Fig. A-1 Typical Straightness Gage

Adjustable rail Reverse reading micrometer heads

Securing screws

600 mm
Lf (excluded
125 mm
fillet length)

Maximum body diameter

plus allowable total camber

9
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 ASME B18.2.3.3M-2007

NONMANDATORY APPENDIX B
BODY POSITION GAGES AND GAGING PROCEDURES

Gages that may be used for checking position of the Lh p D + X

screw body with respect to the thread are illustrated
below in Fig. B-1. Diameter, Dh, of the counterbore or hold in sleeve(s),
In the lower construction, GO thread ring gage, A, is equals the nominal screw diameter, D, plus the posi-
centered on sleeve, B, by means of the positioning plug, tional tolerance, T2 (see Table 1); that is
E, and is secured in position by attachment screws, C.
The ring gage is sent to the maximum pitch diameter
of the screw thread Class 6h. Dh p D + T2
For position of body-to-thread per para. 2.7, gage
length, Lh, is equal to the nominal screw diameter, D, The screw is screwed by hand into the GO thread
plus the transition thread length, X; that is gage for the full length of the thread.

Fig. B-1 Typical Gage

Dh

D Lh
Class 6h GO thread gage
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Optional constructions D Lh

C Dh

0 B
Class 6h max. PD thread Dh ⫺ 0.015 E

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 ASME B18.2.3.3M-2007

M10207
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