unserviceable bolt, you must consider the length of the
bolt. As shown in figure 5-1, the bolt length is the
distance from the tip of the threaded end to the head of
the bolt. Correct length selection is indicated when the
bolt extends through the nut at least two full threads.
See figure 5-2. If the bolt is too short, it will not extend
out of the bolt hole far enough for the nut to be securely
fastened. If it is too long, it may extend so far that it
interferes with the movement of nearby parts.
In addition, if a bolt is too long or too short, its grip
will usually be the wrong length. As shown in figure
5-2, the grip length should be approximately the same
as the thickness of the material to be fastened. If the
grip is too short, the threads of the bolt will extend into
the bolt hole. The bolt may act like a reamer when the
material is vibrating. To prevent this, make certain that
no more than two threads extend into the bolt hole.
Also, make certain that any threads that enter the bolt
hole extend only into the thicker member that is being
fastened. If the grip is too long, the nut will run out of
threads before it can be tightened. In this event, a bolt
with a shorter grip should be used. If the bolt grip
extends only a short distance through the hole, a washer
may be used.
A second bolt dimension that must be considered is
diameter. As shown in figure 5-1, the diameter of the
bolt is the thickness of its shaft.
The results of using a wrong diameter bolt should
be obvious. If the bolt is too big, it cannot enter the bolt
hole. If the diameter is too small, the bolt has too much
play in the bolt hole.
The third and fourth bolt dimensions that should be
considered when you choose a bolt replacement are
head thickness and width. If the head is too thin or too
narrow, it might not be strong enough to bear the load
imposed on it. If the head is too thick or too wide, it
might extend so far that it interferes with the movement
of adjacent parts.
AN bolts come in three head styleshex head,
clevis, and eyebolt. NAS bolts are available in
BOLT GRIP LENGTH CORRECT
BOLT GRIP LENGTH TOO SHORT
BOLT GRIP LENGTH TOO LONG
Figure 5-2.Correct and incorrect grip lengths.
Figure 5-1.Bolt terms and dimensions.