FINAL

December 20, 2006

A Guide for the Development

of
ASME B18 Standards
for
Mechanical Fasteners

ASME B18.12.1 - 2006 Key Words:

Guide, B18 Standards

FINAL: December 20, 2006

Sponsored and Published By

THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS
Three Park Avenue New York, N.Y. 10016-5990
ASME B18.12.1-2006 GUIDE B18 STANDARDS

2
GUIDE B18 STANDARDS ASME 18.12.1-2006

A GUIDE FOR THE DEVELOPMENT OF ASME B18 STANDARDS

FOR MECHANICAL FASTENERS

1. Introductory Notes that standards be written only in inch or only in met-

ric (mm) and that dual dimensions be avoided. This
1.1 Scope is intended to provide a basis for possible global
acceptance of purely metric documents. All dimen-
This guide covers the elements for the com-
sions shall apply before coating and this statement
plete development of B18 standards. It should be
should be included to prevent confusion regarding
understood that only those elements applicable to
any dimensional changes that may occur as a result
the development of any given standard should be
of coating.
adopted. Clearly, not all may be reasonably ap-
plied to any given standard. The discussion of these 1.4 Options
elements is presented in the order they would nor-
mally appear in a given B18 standard and a tem- This paragraph is intended to offer flexibility
plate is included in Appendix A. to the application of the standard. For example,
where special materials, coatings, lubrication, or
1.2 Comparison to ISO Standards packaging may be needed by the purchaser, this
provision should be included in the standard and
Where ISO standards exist, a detailed com- specified by the purchaser on the purchase order.
parison to the ASME metric standard, including each
geometric characteristic, material, range of size, and 1.5 Terminology
performance is suggested to facilitate specification
by respective users. The detail of comparison should This paragraph is intended to reduce the ver-
be included in an appendix while this paragraph in biage in each standard and to focus on a single docu-
the standard identifies the ISO standards for com- ment, namely, ASME B18.12, to provide for con-
parative purposes and refers to the appendix for a sistency in definitions that may have formerly ap-
detailed summary by applicable characteristic. A peared in multiple standards with slight variations.
good example of this comparison may be found in Where terms are not defined in ASME B18.12, they
Appendix IV of ASME B18.2.3.1M. Also, an ex- are included and defined in this paragraph.
ample taken from B18.2.3.4M is included in Ap- 1.5.1 Terminology Referenced
pendix B of this standard for illustrative purposes.
For definitions of terminology not specifi-
1.3 Dimensions cally defined in this standard, refer to ASME B18.12.
A statement indicating that: "unless other- 1.6 Referenced Standards
wise specified, all dimensions are in inches" or that
"all dimensions, unless otherwise specified, are in met- This paragraph is intended to identify all stan-
ric (mm)" should be included. It is recommended dards that are specified or referred to in a given stan-

3
ASME B18.12.1-2006 GUIDE B18 STANDARDS

dard by name, number, and publisher. It should also ASTM F1137, Specification for Phosphate/
state that the latest edition of the listed standard is to Oil and Phosphate/Organic Corrosion
be used, unless a specific date of issue is included in Protective Coatings for Fasteners
the list. Specific dates shall not be listed, unless a ASTM F1941, Specification for Electrode-
posited Coatings on Threaded Fasten-
technical engineering reason has been established
ers [Unified Inch Screw Threads (UN/
necessitating the citing of a specific issue.
UNR)]
Publisher: American Society for Testing and
1.6.1 Example of Referenced Standards Materials (ASTM), 100 Barr Harbor
Drive, West Conshohocken, PA 19428
Standards that are called out should be listed
by issuing source. The most current issue of the
1.7 Related Standards
referenced standard is applicable, unless otherwise
specified by the purchaser. Below is an example: This may list standards and their sources that
are not referred to in the given document but may
Example: cover similar or related products or tests. For ex-
ample, a spring pin standard may list related stan-
Referenced Standards dards for other pins such as clevis, cotter, or dowel
pins. These would be listed in a similar way as shown
Unless otherwise specified, the standards
in paragraph 1.6.1.
referenced shall be the most recent at the
time of order placement.
1.8 Part Identifying Number
ASME B1.1, Unified Inch Screw Threads
(UN and UNR Thread Form) This is a standard "boiler plate" paragraph
ASME B18.12, Glossary of Terms for Me- to refer the specification user to ASME B18.24 and
chanical Fasteners a recommended procedure to establish a part iden-
ASME B18.18.1, Inspection and Quality As- tification number (PIN) applicable to all B18 prod-
surance for General Purpose Fasteners uct standards, typically, paragraph 1.8:
ASME B18.18.2, Inspection and Quality As-
surance for High-Volume Machine As- For a Part Identifying Number, refer to
sembly Fasteners ASME B18.24.
ASME B18.24, Part Identifying Number
(PIN) Code System for B18 Fastener
2. General Data
Products
Publisher: The American Society of Me- This paragraph provides for specification of
chanical Engineers (ASME Interna-
geometry, materials and heat treatment, dimensional
tional), Three Park Avenue, New York,
conformance, quality assurance, workmanship, gag-
NY 10016-5990; Order Department: 22
Law Drive, Box 2300, Fairfield, NJ ing and acceptance procedures, marking require-
07007-2300 ments, and packaging. A review of the template in-
cluded in Appendix A of this guide will help to iden-
ASTM B21, Specification for Naval Brass, tify, for a given product, which of the features should
Rod, Bar, and Shapes necessarily be included.

4
GUIDE B18 STANDARDS ASME 18.12.1-2006

2.1 Heads parallel to the axis of the product from the

top of the head to the bearing surface and
The intention of this paragraph is to describe shall include the thickness of the washer
and identify the head configuration and its dimen- face. Raised grade and manufacturer's iden-
sions and tolerances. A drawing is usually present tification are excluded from head height.
and the dimensions are identified by letters which
are included with a word description in tables to- 2.1.5 True Position of Head. The axis
gether with stated dimensions and tolerances. These of the head shall be located at true posi-
should be specific so that wrench or driver fit is as- tion with respect to the axis of the body
sured. In those products such as pins or studs, which (determined over a distance under the head
have no head configuration, this paragraph should equal to one diameter) within a tolerance
not be applied. A list of seventeen head character- zone having a diameter equivalent to 6%
istics which may be included as appropriate in sub- of the maximum width across flats at maxi-
paragraphs are listed in Appendix A. The following mum material condition.
is an example of typical head characteristics:
2.2 Product Length
Example:
This paragraph would normally define the
2.1.1 Top of Head. Top of head shall be overall product length and tolerances, which are stan-
full form and chamfered or rounded with dard, and a procedure for measurement. Addition-
the diameter of chamfer circle or start of ally, such lengths as the thread length (2.5), grip gag-
rounding being equal to the maximum width ing length, body length, and transition thread length
across flats within a tolerance of minus 15%. (2.6) are often included as subparagraphs to assist
in selection and application.
2.1.2 Width Across Flats. The width
Example:
across flats of heads shall be the distance,
measured perpendicular to the axis of prod- The length of the screw shall be mea-
uct, overall between two opposite sides of sured parallel to the axis of the screw from
the head. the plane of the bearing surface under the
head to the plane of the flat of the point.
2.1.3 Head Taper. Maximum width
across flats shall not be exceeded. No 2.3 Threads
transverse section through the head be-
tween 25% and 75% of actual head height, Most threads are specified by reference to
as measured from the bearing surface, shall ASME B1.1 or ASME B1.13M including a given
be less than the minimum width across pitch and a class of fit. Methods relating to accept-
flats. ability are identified as a given system in ASME B1.3,
and a separate paragraph (2.4) would be used to
2.1.4 Head Height. The head height specify the thread acceptance system. The follow-
shall be that overall distance measured ing is a typical paragraph for thread specification:

5
ASME B18.12.1-2006 GUIDE B18 STANDARDS

Example: the bearing surface of the head to the face

of a nonchamfered or noncounterbored
Threads shall be cut or rolled in ac- standard 3A GO thread ring gage assembled
cordance with ASME B1.1, Unified by hand as far as the thread will permit.
Coarse, Class 2A.
(a) Sizes No. 5 and Smaller. Screws of
2.4 Thread Acceptance Gaging nominal lengths equal to three diameters and
shorter shall have full form threads extend-
Typically, this paragraph would specify ing to within one pitch (thread) of the bear-
thread dimensional acceptability in accordance with ing surface of the head, or closer, if practi-
Gaging System 21 as specified in ASME B1.3 or cable. Nominal lengths greater than three
ASME B1.3M for metric product. However, the diameters, up to and including 1-1/8 in.,
shall have full form threads extending to
user may have specified certain thread characteris-
within two pitches (threads) of the bearing
tics which will require a different acceptance proce-
surface of the head, or closer, if practicable.
dure and this paragraph will usually state System 21, Screws of longer nominal lengths shall, un-
unless otherwise specified. less otherwise specified, have a minimum
length of full form thread of 1 in.
Example:
(b) Sizes No. 6 and Larger. Screws of
Unless otherwise specified by the pur- nominal lengths equal to three diameters and
chaser, gaging for screw thread dimen- shorter shall have full form threads extend-
sional acceptability shall be in accor- ing to within one pitch (thread) of the bear-
dance with Gaging System 21 as speci- ing surface of the head, or closer, if practi-
fied in ASME B1.3M. cable. Nominal lengths greater than three
diameters, up to and including 2 in., shall
2.5 Thread Length have full form threads extending to within
two pitches (threads) of the bearing surface
Thread length is controlled on many bolts of the head, or closer, if practicable. Screws
by the so-called grip gaging length maximum. This of longer nominal lengths shall, unless oth-
paragraph will specify this, if applicable, and sub- erwise specified, have a minimum length of
paragraphs will specify the method or procedure for full form thread of 1.50 in.
measurement. Certain small products, such as ma-
chine screws, may specify the thread length in terms 2.5.2 Body Length
of its approach to the bearing surface of the head by
Body length is the distance, as measured par-
the number of thread pitches.
allel to the axis of the fastener, from the underside of
Example: the head to the last scratch of thread or top of the
extrusion angle.
2.5.1 Machine Screws. Machine screws
shall have thread lengths conforming to the 2.5.3 Grip Gaging Length
following: On screws threaded full length,
the distance to first full form thread shall be This is the distance as measured parallel to
measured, parallel to the axis of screw, from the axis of the fastener from the underside of the

6
GUIDE B18 STANDARDS ASME 18.12.1-2006

head bearing surface to the face of a noncounter- 2.8.1 Reduced Diameter Body
bored or noncountersunk standard Go thread ring
gage which has been assembled by hand as far as These have a body diameter not less than
the thread will permit. the minimum pitch diameter, and not exceeding the
specified minimum full size diameter body.
2.6 Transition Thread Length
2.9 True Position of Tapped Hole
A dimension commonly expressed as a refer-
ence dimension which accounts for the length of in- The axis of a tapped hole in the nut is lo-
complete threads, extrusion angle for rolled threads, cated at true position with respect to the axis of the
and the tolerances on the grip length. It is recom- nut body within a tolerance zone having a diameter
mended that both a rolled and cut thread represen- equal to a given percentage of the the maximum width
tation be present for each threaded product as may across flats.
be applicable. Often, the transition thread length
may be expressed as the number of pitches for a 2.10 Nut Thickness
given thread.
The nut thickness is the overall distance
2.7 Point measured parallel to the axis of the nut, from the top
of the nut to the bearing surface. This includes the
All screws have a point to facilitate starting thickness of the washer face where provided. Raised
or to apply pressure (compression). Such points markings are not included in nut thickness.
are called out as flat, oval, cup, cone, or half dog.
In other cases, points are described as chamfered 2.11 Prongs
or rounded from a given diameter below the minor
thread diameter, and having a length which is a mul- Cotter pins have a preferred point extended
tiple of the thread pitch. The length of the point prong having a square or hammered lock design
measured to the first full formed thread at the major unless otherwise specified.
diameter may be specified in the dimensional table
for a given screw. Rivets and pins may have sheared 2.12 Taper
ends or may be crowned or chamfered as specified
in the applicable product standard. Point features Taper pins provide for a taper on the diam-
not defined in a given product standard are at the eter based on a unit of length and for a given toler-
discretion of the manufacturer. ance.

2.8 Body Diameter 2.13 Straightness

This is generally the unthreaded portion of a A rail gage or a sleeve gage is used to as-
shank whose diameter is the maximum or minimum sure shank straightness or camber limitations included
limit or the basic size with plus and minus tolerances within respective product standards. At maximum
applied. It is often used to "account" for any swell, material condition, maximum camber per unit length
fin, or die seam under the head from manufacture. is generally specified for given product lengths.

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ASME B18.12.1-2006 GUIDE B18 STANDARDS

2.14 Finishes 2.17 Grade or Property Class Symbol

Dimensions for products and dimensional These marks are mandated by the applicable
characteristics are usually specified for plain finish. material and performance specification such as those
If a coating is specified, it should be in accordance found in ASTM or SAE. Inch series products are
with a class or condition specified in an applicable generally related to Grades 2, 5, and 8; while metric
standard such as an ASTM standard. series products are related to property classes rang-
ing from 4.6 to 12.9. A typical callout is as follows:
2.15 Workmanship Example:
A clause which assures that a product will Each bolt shall be marked in accordance
be visually free of irregularities that would impact its with the requirements of ASTM A449.
fit, form, or function.
2.18 Manufacturer's or Source Symbol
2.16 Designation
These marks are mandated by the standards
This provides a standard method for call out that specify material, mechanical, and performance
in communications. requirements. For fasteners subject to the Fastener
Quality Act requirements, the marks used are to be
Example: fully traceable and registered by the manufacturer
with the U.S. Patent and Trademark Office. This
Product name, ASME dimensional standard,
registration is required by the Fastener Quality Act.
diameter-pitch, length, mechanical or per-
formance standard, finish type and thick-
ness including applicable standard. 2.19 Inspection and Quality Assurance

Examples: ASME has seven quality assurance docu-

ments (ASME B18.18.1 thru B18.18.7) for me-
Heavy hex nut, ASME B18.2.6, Unified 1/2- chanical fasteners. ASTM has a document (ASTM
13, ASTM A563 Grade C, Plain Finish F1470) to determine sample sizes for mechanical
properties using detection or prevention techniques.
Hex cap screw, ASME B18.2.1, Unified 3/8-
16 x 4, ASTM A354 Grade BD, type Fe/Zn- The standard should be called out in this paragraph,
5A, ASTM F1941 which is the most basic for the given product, with
the option for alternative specification left to the pur-
Metric hex cap screws, ASME B18.2.3.1M, chaser.
M16 x 2 x 100, ASTM F568M Class 10.9,
Plain Finish Example:

Metric hex nuts Style 2, ASME B18.2.4.2M, Unless otherwise specified, products shall
M10 x 1.5, ASTM A563M Class 9, Plain Fin- be furnished in accordance with ASME
ish B18.18.2.

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GUIDE B18 STANDARDS ASME 18.12.1-2006

2.20 Designated Dimensional Conformance Steel Nuts, ASTM F738M - Stainless Steel Met-
ric Bolts, Screws and Studs, and ASTM F836M -
This paragraph is intended to designate the Stainless Steel Metric Nuts define basic material
characteristics and inspection level established by and processing requirements.
the technical committee. These are characteristics
that have significant impact on the fit, form, and func- 2.21.3 Nonferrous. Includes materials such as
tion of the product, should they be found to be non- brass, titanium, copper, nickel, or aluminum which,
conforming. with various alloys, are defined in such standards as
ASTM F468 - Nonferrous Bolts, Hex Cap Screws,
2.20.1 Dimensional Conformance Example and Studs for General Use or ASTM F468M -
Nonferrous Bolts, Hex Cap Screws, and Studs for
Socket button head cap screws shall have General Use (Metric).
the following designated characteristics inspected to
ASME B18.18.2 to the inspection levels shown: 2.21.4 Total Case Depth. Is a distance measured
perpendicularly from the surface of a hardened case
Characteristic Inspection Level to a point where differences in chemical or physical
properties of the case and core can no longer be
Threads C distinguished. SAE J423, ASTM F2328, ASTM
Head Diameter C F2328M, or SAE J121M specify a method to ac-
Socket Size (gaged) C curately measure the case depth.
Length C
Fillet Transition Diameter C 2.21.5 Surface Hardness. The method to measure
surface hardness involves the use of an indenter. For
2.21 Materials and Heat Treatment routine checks, a Knoop or pyramid indenter may be
used. The referee method involves one of these in-
Requirements are usually found in the ap- denters and a given load. See paragraph 3.4 Surface
propriate ASTM, IFI, or SAE standard. Hardness after Tempering of SAE J933.

2.21.1 Steel. Carbon and alloy steel requirements 2.21.6 Core Hardness. This requires cutting a
are defined in such standards as ASTM A307 - Car- transverse section through the thread of a bolt, screw,
bon Steel Bolts and Studs, 60,000 PSI Tensile or stud at a distance one diameter from the point or
Strength, ASTM A449 - Quench and Tempered
end of the product. Four readings at 90 degree in-
Steel Bolts and Studs, and ASTM A563 - Carbon
crements are averaged to establish a value. ASTM
and Alloy Steel Nuts, ASTM A563M - Carbon
and Alloy Steel Metric Nuts, and ASTM F568M - F606, ASTM F606M, and SAE J1237 describe a
Carbon and Alloy Steel Externally Threaded procedure for this measurement.
Fasteners.
2.21.7 Microstructure. This examination involves
2.21.2 Corrosion Resistant. A term used to de- a microscopic look at the metal structure of a pol-
scribe a characteristic of the basic material or coat- ished and etched specimen using magnifications in
ing found in or on a fastener. Such standards as excess of 10x. Such structures are pictured in the
ASTM F593 - Stainless Steel Bolts, Hex Cap appendix of SAE J78, Self-Drilling Tapping
Screws and Studs and ASTM F594 - Stainless Screws.

9
ASME B18.12.1-2006 GUIDE B18 STANDARDS

3. Performance Requirements and Tests applying a load to the head of a screw or bolt by
reaching a specified angle between the plane of the
A given B18 standard may specify mechani- head bearing surface and the shank without head
cal or performance characteristics for a product. separation.
Additionally, the standard may specify a test proce-
dure to establish that a given fastener meets the ap- 3.4 Drive Test
plicable mechanical or performance requirements.
A listing of the mechanical and performance char- Used to establish that the threads of a screw
acteristics generally included in some B18 standards will, without deformation of its threads, form mating
is shown in Appendix A. threads in a specified test plate at given rotational
speeds.
3.1 Tensile Strength
3.5 Torsional Test
This is a requirement, usually stated as a
minimum, to which a product is processed to meet. In a specified test device, a screw is suitably
Often, for carbon and alloy steel product, it is torqued to failure. The failure torque should meet a
broadly referred to as property class or strength given minimum requirement based on thread form.
grade. The exceptions to this rule are found in
ASTM A307 and ASTM A490. Both specify a 3.6 Hardness
maximum tensile strength in addition to the specified
minimum. Values may be required at the core, sur-
face, or at the total case depth depending upon the
3.2 Proof Load specification requirement. These may be related to
tensile strength in screws that are too short to ad-
Is usually stated to be an absolute value that equately tensile test.
a product must meet without dimensional change or
thread deformation. It is this value that is used with 3.7 Hydrogen Embrittlement
a factor of safety for design purposes.
Products with high hardness and electro-
3.3 Ductility Test plated fasteners often require testing for this fail-
ure mode. This paragraph should specify appli-
A test that is used to assure the integrity of cable tests and steps to be followed in processing
the head to shank junction. It is usually done by to reduce potential failure.

10
GUIDE B18 STANDARDS ASME 18.12.1-2006

APPENDIX A
STANDARDS TEMPLATE

Foreword 2.5.3 grip gaging length

2.6 Transition Thread Length
1. Introductory Notes 2.7 Point
2.8 Body Diameter
1.1 Scope 2.8.1 reduced diameter body
1.2 Comparison to ISO Standards 2.9 True Position of Tapped Hole
1.3 Dimensions 2.10 Nut Thickness
1.4 Options 2.11 Prongs
1.5 Terminology 2.11.1 preferred points
1,5.1 terminology referenced 2.11.2 prong alignment
1.6 Referenced Standards 2.12 Taper
1.6.1 example of referenced 2.13 Straightness
standards 2.14 Finishes
1.7 Related Standards 2.15 Workmanship
1.8 Part Identifying Number 2.16 Designation
2.17 Grade or Property Class Symbol
2. General Data 2.18 Manufacturer’s or Source Symbol
2.19 Inspection and Quality Assurance
2.1 Heads 2.20 Designated Dimensional
2.1.1 top of head Conformance
2.1.2 width across flats 2.20.1 dimension conformance
2.1.3 head taper examples
2.1.4 head height 2.21 Materials and Heat Treatment
2.1.5 true position of head 2.21.1 steel
2.1.6 width across corners 2.21.2 corrosion-resistant
2.1.7 bearing surface 2.21.3 nonferrous
2.1.8 chamfer 2.21.4 total case depth
2.1.9 indent 2.21.5 surface hardness
2.1.10 corner fill 2.21.6 core hardness
2.1.11 recess depth 2.21.7 microstructure
2.1.12 slot depth 2.21.8 surface roughness
2.1.13 feature positional tolerances
2.1.14 underhead fillet 3. Performance Requirements and Tests
2.1.15 gaging of head
2.1.16 wrenching height 3.1 Tensile Strength
2.1.17 head periphery 3.2 Proof Load
2.2 Product Length
3.3 Ductility Test
2.3 Threads
2.4 Thread Acceptance Gaging 3.4 Drive Test
2.5 Thread Length 3.5 Torsional Test
2.5.1 machine screws 3.6 Hardness
2.5.2 body length 3.7 Hydrogen Embrittlement

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ASME B18.12.1-2006 GUIDE B18 STANDARDS

NONMANDATORY APPENDIX B
COMPARISON WITH ISO STANDARDS
(This Appendix is not an integral part of ASME B18.2.3.4M-2001 and is included for information purposes only.)

This Appendix describes the technical differ- A5 POSITION OF HEAD

ences between ASME B18.2.3.4M-2001 and ISO
4162: 1990, its draft revision, ISO/DIS 4162.2: ASME B18.2.3.4M, para. 11 and Table 2
1998, and related ISO standards. specify positional tolerance at maximum material
condition, as in ISO/DIS 4759-1: May 1998, in-
A1 PRODUCT NAMES BOLT AND SCREW stead of regardless of feature size, as in ISO 4759/
I-1978. ISO/DIS 4759-1: May 1998 also speci-
Of the products named hex flange screw per fies position of the flange diameter with respect to
ASME B18.2.3.4M, those that are threaded full the shank, which is not specified in ASME
length would be named hexagon screw with flange B18.2.3.4M.
per ISO 1891, but those that are not threaded full
length are named hexagon flange bolt per ISO A6 BEARING SURFACE
4162: 1990, and hexagon bolt with flange per ISO
1891 and ISO/DIS 4162.2: 1998. ASME B18.2.3.4M, para. 13 and Table 5
specify bearing surface concavity of 0.75±0.50 deg,
A2 HEAD HEIGHT AND WRENCHING as in ISO/DIS 4162.2: 1998, which is a draft revi-
HEIGHT sion. ISO 4162: 1990 specifies 0 to 1 degrees 30
minimum (0.75±0.75 degrees). ISO/DIS 4759-1:
May 1998 specifies straightness of radial lines on
ASME B18.2.3.4M Table 5 specifies maxi-
the bearing surface, which is not specified in ASME
mum head heights for M6, M12, and M16, and mini-
B18.2.3.4M. ASME B18.2.3.4M, Table 2 values
mum wrenching height for M16, in agreement with
for circular runout of the bearing circle are greater
ISO/DIS 4162.2; 1998, which are increased from
than those in ISO 4759/I-1978 or ISO/DIS 4759-
those specified in ISO 4162: 1990.
1: May 1998.
A3 MAXIMUM WIDTH ACROSS COR-
A7 FILLETS
NERS
ASME B18.2.3.4M, Table 3 minimum fillet
ASME B18.2.3.4M, Table 5 maximum width transition diameters and shorter maximum fillet
across corners is not specified in ISO 4162. In- lengths for screws threaded full length are not speci-
stead, ISO/DIS 4759-1: May 1998 would control fied in ISO 4162. For Type U fillet, the radius of
the shape of the hexagon by zero positional toler- the fillet extension, r4 reference in ISO 4162, is not
ance at maximum material condition, which is not specified in ASME B18.2.3.4M.
specified in ASME B18.2.3.4M.
A8 BODY DIAMETER FOR SCREWS
A4 GAGING OF HEX FLANGE HEAD THREADED FULL LENGTH
ISO/DIS 4162.2 would specify a gage C for ASME B18.2.3.4M, Tables 3 and 4 minimum
gaging flange thickness, which is not included in diameters of unthreaded shank for screws threaded
ASME B18.2.3.4M. full length are not specified in ISO 4162.

12
GUIDE B18 STANDARDS ASME 18.12.1-2006

A9 REDUCED DIAMETER BODY ASME B18.2.3.4M, Table 10 maximum

unthreaded lengths under the head of screws shorter
ASME B18.2.3.4M, Table 6 maximum and than 2D differ from ISO 3508.
minimum diameters of reduced body differ from ISO
4162 "d2 is approximately equal to the pitch diam- A13 TRANSITION THREADS
eter (rolling diameter)." The limits specified in ASME
B18.2.3.4M Table 6 were proposed to ISO/TC2/ ASME B18.2.3.4M, para. 20.4 specification
WG2 in May 1995, but ISO/TC2/WG2 was not on root contour of transition threads is not in ISO
willing to specify limits for the rolling diameter. 4162.

A10 POINT A14 POSITION OF BODY-TO-THREAD

Coaxiality or position of the body with respect

ASME B18.2.3.4M, para. 17 and Table 5
to the thread, specified in ISO 4759/I or ISO/DIS
optional rounded point is not in ISO 4162, but Table
4759-1, is not specified in ASME B18.2.3.4M.
8 agrees with ISO 4753.
A15 MARKING
A11 STRAIGHTNESS
ASME B18.2.3.4M, para. 22 allows mark-
ASME B18.2.3.4M specifies straightness at ings on the top of the flange but not on the side of
maximum material condition, as in ISO/DIS 4759- the head, as alternatives to markings on the top of
1: May 1998, instead of regardless of feature size, the head, while ISO 898-1 allows markings on the
as in ISO 4759/I-1978. The formula in ASME side of the head but not on the top of the flange.
B18.2.3.4M results in straightness tolerance zone ASME B18.2.3.4M, para. 22 dimensions of head
diameters that are smaller for lengths 12 mm and markings are not specified in ISO 4162 or ISO 898-1.
shorter, and larger for lengths 16 mm and longer,
than those in ISO 4759/I-1978 or ISO/DIS 4759- A16 INSPECTION AND QUALITYASSURANCE
1: May 1998.
ASME B18.2.3.4M, paras. 25 and 26 inspec-
A12 GRIP LENGTH FOR SCREWS tion and quality assurance provisions differ from those
THREADED FULL LENGTH in ISO 4162.

13