General Purpose Bolts.
The mechanics and appearance of general
purpose bolts and their accompanying washer and bolt combinations are
not discussed here.
They are described in detail in FM 1-563
(Fundamentals of Airframe Maintenance).
The discussion here is
limited to less familiar special-purpose bolts in general use in Army
aircraft. These are Huck lock bolts and Jo-Bolts. Each is described
in the paragraphs that follow.
Huck Lock Bolt. The Huck lock bolt combines the features of a high
strength bolt and a rivet, with advantages over each. The Huck lock
bolt is generally used in wing splices, landing gear, fuel cell
fittings, longerons, beams, skin splice plates, and other major
structural attachments. It is more easily and quickly installed than
the conventional rivet or bolt, and it does not require lock washers,
Like the rivet, the lock bolt is
installed with a pneumatic or pull gun. The most commonly used Huck
lock bolts are the pull, stump, and blind types, shown in Figure
Common features of the three are the annular (circular or
ringed) locking grooves on the pin and the locking collar. Each one
is discussed in the following paragraphs.
Pull-type. The pull-type lock bolt is mainly used in primary and
secondary structural members.
It is installed rapidly and has
approximately one-half the weight of an equivalent general-purpose
bolt and nut. These bolts are available with modified brazier, pan,
and countersunk heads.
A special pneumatic pull gun is required to
install this lock bolt.
The installation can be made by one man
because bucking is not needed.
The stump-type lock bolt, although not having the
extended stem with pull grooves, is a companion fastener to the pull-
type lock bolt. It is used primarily where clearance will not permit
effective installation of the pull type.
These bolts are also
available with modified brazier, pan, and countersunk heads.
stump-type lock bolt installation is made with a standard pneumatic
riveting gun, a hammer set for swaging the collar into the pin-
locking grooves, and bucking bar.
Blind-type. The blind-type lock bolt comes as a complete unit or
assembly, and it has exceptional strength and sheet pull-together
These lock bolts are used where only one side of
the work is accessible and generally where it is difficult to drive a