TM 1-1500-204-23-6
Figure 2-2. Hexagon Head Bolt Identification
e.
Hexagon Head Bolts. The standard aircraft
machine bolt (hexagon head) is an all-purpose structural
bolt used for general applications involving tension and
shear loads. Steel bolts smaller than number 10 and
aluminum alloy bolts smaller than 1/4 inch are easily
overstressed at assembly and are not used in primary
structures.
(1) Material. Bolts are made of cadmium- or
zinc-plated corrosion-resistant steel, corrosion-resistant
steel, or anodized aluminum alloy.
(2) AN bolt part number. The AN bolt code
designation indicates type of bolt, diameter, material,
overall length, and if the head or shank is drilled. See
figure 2-2 and refer to tables 2-2 through 2-5.
f.
Drilled Head Bolts. Drilled head bolts, as
shown in figure 2-3, differ from the standard hexagon
head bolts. The drilled head bolt has a deeper head,
which is drilled for securing with lockwire. Each face of
the bolt head is drilled. Use discrimination when
substituting drilled head bolts for hexagon head bolts.
When drilled head bolts are used as
Figure 2-3. Drilled Head Bolt
capscrews, spring lockwashers may be used when
specified
g.
Close Tolerance Bolts. Close tolerance,
hexagon-head, and 100-degree countersunk bolts are
used in aircraft fabrication where bolted joints are
subject to severe load reversals and vibration The bolt
shanks are made to close tolerance, permitting a very
close fit with the use of reamers. Use such bolts to
eliminate lost motion in control systems, etc. Hexagon
head
bolts
are
shown
in
figure
2-2,100-degree
countersunk bolts are shown in figure 2-4. Use an
internal hexagonal, Phillips or Frearson recess-type
wrench for turning counter-sunk head bolts.
Figure 2-4. Countersunk Close Tolerance Bolt
2-16
