9/8/98 AC 43.
13-1B
TABLE 7-1. Recommended torque values (inch-pounds).
CAUTION
THE FOLLOWING TORQUE VALUES ARE DERIVED FROM OIL FREE CADMIUM PLATED THREADS.
TORQUE LIMITS RECOMMENDED FOR INSTAL- MAXIMUM ALLOWABLE TIGHTENING
LATION (BOLTS LOADED PRIMARILY IN SHEAR) TORQUE LIMITS
Thread Size Tension type nuts Shear type nuts MS20364 Nuts MS20365 and Nuts MS20364 and
MS20365 and AN310 and AN320 (24,000 psi in AN310 (90,000 psi in AN320 (54,000 psi in
(40,000 psi in bolts) bolts) bolts) bolts)
FINE THREAD SERIES
8-36 12-15 7-9 20 12
10-32 20-25 12-15 40 25
1/4-28 50-70 30-40 100 60
5/16-24 100-140 60-85 225 140
3/8-24 160-190 95-110 390 240
7/16-20 450-500 270-300 840 500
1/2-20 480-690 290-410 1100 660
9/16-18 800-1000 480-600 1600 960
5/8-18 1100-1300 600-780 2400 1400
3/4-16 2300-2500 1300-1500 5000 3000
7/8-14 2500-3000 1500-1800 7000 4200
1-14 3700-5500 2200-3300* 10,000 6000
1-1/8-12 5000-7000 3000-4200* 15,000 9000
1-1/4-12 9000-11,000 5400-6600* 25,000 15,000
COARSE THREAD SERIES
8-32 12-15 7-9 20 12
10-24 20-25 12-15 35 21
1/4-20 40-50 25-30 75 45
5/16-18 80-90 48-55 160 100
3/8-16 160-185 95-100 275 170
7/16-14 235-255 140-155 475 280
1/2-13 400-480 240-290 880 520
9/16-12 500-700 300-420 1100 650
5/8-11 700-900 420-540 1500 900
3/4-10 1150-1600 700-950 2500 1500
7/8-9 2200-3000 1300-1800 4600 2700
The above torque values may be used for all cadmium-plated steel nuts of the fine or coarse thread series which
have approximately equal number of threads and equal face bearing areas.
* Estimated corresponding values.
7-44. CLOSE-TOLERANCE BOLTS. of bolt may require light tapping with a mallet
Close-tolerance, hex head, machine bolts to set the bolt shank into the bolt hole.
(AN173 through AN186), 100-degree counter-
sunk head, close-tolerance, high-strength bolts NOTE: Elimination of friction in in-
(NAS333 through NAS340), hex head, close- terference fit applications may some-
tolerance, short thread, titanium alloy bolts times be attained by placing the bolt
(NAS653 through NAS658), 100-degree in a freezer prior to installation.
countersunk flathead, close-tolerance titanium When this procedure is used, the bolt
alloy bolts (NAS663 through NAS668), and should be allowed to warm up to am-
drilled hex head close-tolerance titanium alloy bient temperature before torquing.
bolts (NAS673 through NAS678), are used in
applications where two parts bolted together CAUTION: Caution must be exer-
are subject to severe load reversals and vibra- cised in the use of close-tolerance bolts
tion. Because of the interference fit, this type for all critical applications, such as
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AC 43.13-1B 9/8/98
landing gear, control systems, and MS9039), and drilled twelve point head ma-
helicopter rotary controls. Do not chine bolts (MS9088 through MS9094), are
substitute for close-tolerance fasteners similar to the (NAS624 through NAS644); but
without specific instructions from the are made from different steel alloys, and their
aircraft manufacturer or the FAA. shanks have larger tolerances.
7-45. INTERNAL WRENCHING BOLTS 7-48. CLOSE-TOLERANCE SHEAR
(NAS144 THROUGH NAS158 AND NAS172 BOLTS (NAS464). These bolts are designed
THROUGH NAS176). These are high- for use where stresses normally are in shear
strength bolts used primarily in tension appli- only. These bolts have a shorter thread than
cations. Use a special heat-treated washer bolts designed for torquing.
(NAS143C) under the head to prevent the
large radius of the shank from contacting only 7-49. NAS6200 SERIES BOLTS. These
the sharp edge of the hole. Use a special heat- are close tolerance bolts and are available in
treated washer (NAS143) under the nut. two oversized diameters to fit slightly elon-
gated holes. These bolts can be ordered with
7-46. INTERNAL WRENCHING BOLTS an “X” or “Y” after the length, to designate the
(MS20004 THROUGH MS20024) AND SIX oversized grip portion of the bolt (i.e.,
HOLE, DRILLED SOCKET HEAD BOLTS NAS6204-6X for a 1/4 inch bolt with a
(AN148551 THROUGH AN149350). These 1/64 inch larger diameter). The elongated hole
are very similar to the bolts in paragraph 7-45, may have to be reamed to insure a good fit.
except these bolts are made from different al-
loys. The NAS144 through NAS158 and 7-50. CLEVIS BOLTS (AN21
NAS172 through NAS176 are interchangeable THROUGH AN36). These bolts are only
with MS20004 through MS20024 in the same used in applications subject to shear stress, and
thread configuration and grip lengths. The are often used as mechanical pins in control
AN148551 through AN149350 have been su- systems.
perseded by MS9088 through MS9094 with
the exception of AN149251 through 149350, 7-51. EYEBOLTS (AN42 THROUGH
which has no superseding MS standard. AN49). These bolts are used in applications
where external tension loads are to be applied.
7-47. TWELVE POINT, EXTERNAL The head of this bolt is specially designed for
WRENCHING BOLTS, (NAS624 the attachment of a turnbuckle, a clevis, or a
THROUGH NAS644). These bolts are used cable shackle. The threaded shank may or may
primarily in high-tensile, high-fatigue strength not be drilled for safetying.
applications. The twelve point head, heat-
resistant machine bolts (MS9033 through 7-62. [RESERVED.]
7-52.
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9/8/98 AC 43.13-1B
SECTION 4. NUTS
7-63. GENERAL. Aircraft nuts are avail- e. Metal locknuts are constructed with
able in a variety of shapes, sizes, and material either the threads in the locking insert, out-of-
strengths. The types of nuts used in aircraft round with the load-carrying section, or with a
structures include castle nuts, shear nuts, plain saw-cut insert with a pinched-in thread in the
nuts, light hex nuts, checknuts, wingnuts, and locking section. The locking action of the all-
sheet spring nuts. Many are available in either metal nut depends upon the resiliency of the
self-locking or nonself-locking style. Typical metal when the locking section and load-
nut types are shown in table 7-13. Refer to the carrying section are engaged by screw threads.
aircraft manufacturer’s structural repair man- Metal locknuts are primarily used in high tem-
ual, the manufacturer’s engineering depart- perature areas.
ment, or the FAA, before replacing any nut
with any other type. f. Fiber or nylon locknuts are con-
structed with an unthreaded fiber or nylon
7-64. SELF-LOCKING NUTS. These nuts locking insert held securely in place. The fiber
are acceptable for use on certificated aircraft or nylon insert provides the locking action be-
subject to the aircraft manufacturer’s recom- cause it has a smaller diameter than the nut.
mended practice sheets or specifications. Two Fiber or nylon self-locking nuts are not in-
types of self-locking nuts are currently in use, stalled in areas where temperatures exceed
the all-metal type, and the fiber or nylon type. 250 °F. After the nut has been tightened, make
sure the bolt or stud has at least one thread
a. DO NOT use self-locking nuts on parts showing past the nut. DO NOT reuse a fiber
subject to rotation. or nylon locknut, if the nut cannot meet the
minimum prevailing torque values. (See ta-
b. Self-locking castellated nuts with ble 7-2.)
cotter pins or lockwire may be used in any
system. g. Self-locking nut plates are produced in
a variety of forms and materials for riveting or
c. Self-locking nuts should not be used welding to aircraft structures or parts. Certain
with bolts or screws on turbine engine air- applications require the installation of self-
planes in locations where the loose nut, bolt, locking nuts in channel arrangement permit-
washer, or screw could fall or be drawn into ting the attachment of many nuts in a row with
the engine air intake scoop. only a few rivets.
d. Self-locking nuts should not be used 7-65. NUT IDENTIFICATION FIN-
with bolts, screws, or studs to attach access ISHES. Several types of finishes are used on
panels or doors, or to assemble any parts that self-locking nuts. The particular type of finish
are routinely disassembled before, or after each is dependent on the application and tempera-
flight. They may be used with anti-friction ture requirement. The most commonly used
bearings and control pulleys, provided the in- finishes are described briefly as follows.
ner race of the bearing is secured to the sup-
porting structure by the nut and bolt.
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AC 43.13-1B 9/8/98
TABLE 7-2. Minimum prevailing torque values for re- (3) Iridescent Dichromate. Cadmium-
used self-locking nuts. plated work is dipped in a solution of sodium
FINE THREAD SERIES dichromate and takes on a surface film of basic
MINIMUM PREVAILING chromium chromate which resists corrosion.
THREAD SIZE TORQUE Finish is yellow to brown in color.
7/16 - 20 8 inch-pounds
1/2 - 20 10 inch-pounds NOTE: Cadmium-plated nuts are re-
9/16 - 18 13 inch-pounds
stricted for use in temperatures not to
5/8 -18 18 inch-pounds
3/4 - 16 27 inch-pounds exceed 450 °F. When used in tem-
7/8 - 14 40 inch-pounds peratures in excess of 450 °F, the
1 - 14 55 inch-pounds cadmium will diffuse into the base ma-
1-1/8 - 12 73 inch-pounds terial causing it to become very brittle
1-1/4 - 12 94 inch-pounds
and subject to early failure.
COARSE THREAD SERIES
THREAD SIZE MINIMUM PREVAILING
TORQUE
b. Silver plating. Silver plating is applied
7/16 - 14 8 inch-pounds to locknuts for use at higher temperatures.
1/2 - 13 10 inch-pounds Important advantages are its resistance to ex-
9/16 - 12 14 inch-pounds treme heat (1,400 °F) and its excellent lubri-
5/8 - 11 20 inch-pounds cating characteristics. Silver resists galling
3/4 - 10 27 inch-pounds and seizing of mating parts when subjected to
7/8 - 9 40 inch-pounds
1-8 51 inch-pounds
heat or heavy pressure.
1-1/8 - 8 68 inch-pounds
1-1/4 - 8 88 inch-pounds c. Anodizing for Aluminum. An inor-
ganic oxide coating is formed on the metal by
a. Cadmium-Plating. This is an electro- connecting the metals and anodes in a suitable
lytically deposited silver-gray plating which electrolyte. The coating offers excellent corro-
provides exceptionally good protection against sion resistance and can be dyed in a number of
corrosion, particularly in salty atmosphere, but colors.
is not recommended in applications where the
temperature exceeds 450 °F. The following d. Solid Lubricant Coating. Locknuts
additional finishes or refinements to the basic are also furnished with molybdenum disulfide
cadmium can be applied. for lubrication purposes. It provides a clean,
dry, permanently-bonded coating to prevent
(1) Chromic Clear Dip. Cadmium sur- seizing and galling of threads. Molybdenum
faces are passivated, and cyanide from the disulfide is applied to both cadmium and sil-
plating solution is neutralized. The protective ver-plated parts. Other types of finishes are
film formed gives a bright, shiny appearance, available, but the finishes described in this
and resists staining and finger marks. chapter are the most widely used.
(2) Olive Drab Dichromate. Cadmium- 7-66. CASTLE NUT (AN310). The castle
plated work is dipped in a solution of chromic nut is used with drilled shank hex head bolts,
acid, nitric acid, acetic acid, and a dye which clevis bolts, drilled head bolts, or studs that are
produces corrosion resistance. subjected to tension loads. The nut has slots or
castellations cut to accommodate a cotter pin
or safety wire as a means of safetying.
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9/8/98 AC 43.13-1B
7-67. CASTELLATED SHEAR NUT 7-71. WINGNUTS (AN350). The wingnut
(AN320). The castellated shear nut is de- is used where the desired torque is obtained by
signed for use with hardware subjected to use of the fingers or handtools. Wingnuts are
shear stress only. normally drilled to allow safetying with safety
wire.
7-68. PLAIN NUT (AN315 AND AN335).
The plain nut is capable of withstanding large 7-72. SHEET SPRING NUTS (AN365).
tension loads; however, it requires an auxiliary Sheet spring nuts are commonly called speed
locking device, such as a checknut or safety nuts. They are used with standard and sheet
wire. Use of this type on aircraft structures is metal self-tapping screws in nonstructural ap-
limited. plications. They are used to support line and
conduit clamps, access doors, etc. Their use
7-69. LIGHT HEX NUTS (AN340 AND should be limited to applications where they
AN345). These nuts are used in nonstructural were originally used in assembly of the air-
applications requiring light tension. Like the craft.
AN315 and AN335, they require a locking de-
vice to secure them. 7-84. RESERVED.
7-73.
7-70. CHECKNUT (AN316). The checknut
is used as a locking device for plain nuts,
screws, threaded rod ends, and other devices.
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