an inch. For instance, in figure 2-23, the last digit of
the series number is 4; therefore, this bolt is 4/16 of an
inch (1/4 of an inch) in diameter. In the case of a
series number ending in 0, for instance AN30, the 0
stands for 10, and the bolt has a diameter of 10/16 of
an inch (5/8 of an inch).
Refer again to figure 2-23, and observe that a dash
follows the series number. When used in the part
numbers for general-purpose AN bolts, clevis bolts,
and eyebolts, this dash indicates that the bolt is made
of carbon steel. With these types of bolts, the letter C,
used in place of the dash, means corrosion-resistant
steel. The letter D means 2017 aluminum alloy. The
letters DD stand for 2024 aluminum alloy. For some
bolts of this type, a letter H is used with these letters
or with the dash. If it is so used, the letter H shows
that the bolt has been drilled for safetying.
Next, observe the number 20 that follows the
dash. This is called the dash number. It represents
the bolts grip (as taken from special tables). In this
instance the number 20 stands for a bolt that is 2 1/32
The last character in the AN number shown in
figure 2-23 is the letter A. This signifies that the bolt
is not drilled for cotter pin safetying. If no letter were
used after the dash number, the bolt shank would be
drilled for safetying.
NAS Part Number.Another series of bolts
used in aircraft construction is the NAS. See
In considering the NAS 144-25 bolt
(special internal-wrenching type), observe that the
bolt identification code starts with the letters NAS.
Next, the series has a three-digit number, 144, The
first two digits (14) show the class of the bolt. The
next number (4) indicates the bolt diameter in
sixteenths of an inch. The dash number (25) indicates
bolt grip in sixteenths of an inch.
Figure 2-24.NAS bolt part number breakdown.
Figure 2-25.MS bolt part number breakdown.
MS Part Number.MS is another series of bolts
used in aircraft construction. In the part number
shown in figure 2-25, the MS indicates that the bolt is
a Military Standard bolt. The series number (20004)
indicates the bolt class and diameter in sixteenths of
an inch (internal-wrenching, 1/4-inch diameter). The
letter H before the dash number indicates that the bolt
has a drilled head for safetying. The dash number (9)
indicates the bolt grip in sixteenths of an inch.
Aircraft nuts differ in design and material, just as
bolts do, because they are designed to do a specific
job with the bolt. For instance, some of the nuts are
made of cadmium-plated carbon steel, stainless steel,
brass, or aluminum alloy. The type of metal used is
not identified by markings on the nuts themselves.
Instead, the material must be recognized from the
luster of the metal.
Nuts also differ greatly in size and shape. In spite
of these many and varied differences, they all fall
under one of two general groups: self-locking and
nonself-locking. Nuts are further divided into types
such as plain nuts, castle nuts, check nuts, plate nuts,
channel nuts, barrel nuts, internal-wrenching nuts,
external-wrenching nuts, shear nuts, sheet spring
nuts, wing nuts, and Klincher locknuts.
nuts require the use of a separate locking device for
security of installation.
There are several types of
these locking devices mentioned in the following
paragraphs in connection with the nuts on which they
are used. Since no single locking device can be used
with all types of nonself-locking nuts, you must select
one suitable for the type of nut being used.
SELF-LOCKING NUTS.Self-locking nuts
provide tight connections that will not loosen under
Self-locking nuts approved for use on
aircraft meet critical strength, corrosion-resistance,