countersunk, internal wrenching, and hex head styles.
MS bolts come in internal wrenching and hex head
styles. Head markings indicate the material of which
standard bolts are made. Head markings may indicate if
the bolt is classified as a close-tolerance bolt. See figure
5-3. Additional information, such as bolt diameter, bolt
length, and grip length, may be obtained from the bolt
The most common threaded fastener used in
aircraft construction is the screw. The three most used
types are the machine screw, structural screw, and the
self-tapping screw, as shown in figure 5-4. Figure 5-4
also shows the three head slotsstraight, Phillips, and
Reed and Prince.
Structural screws are used for assembly of
structural parts, as are structural bolts. They are made
of alloy steel and are properly heat-treated. Structural
screws have a definite grip length and the same shear
and tensile strengths as the equivalent size bolt. They
differ from structural bolts only in the type of head.
COUNTERSUNK HEAD BOLT
INTERNAL WRENCHING BOLT
DRILLED HEX HEAD BOLT
Figure 5-3.Types of bolts and bolt head markings.