movable jaw on a pipe wrench is pivoted to permit a
gripping action on the work. This tool must be used
with discretion, as the jaws are serrated and always
make marks on the work unless adequate precautions
are observed. The jaws should be adjusted so the bite on
the work will be taken at about the center of the jaws.
The strap wrench (fig. 1-39) is used for turning pipe
or cylinders where you do not want to mar the surface
of the work. To use this wrench, the webbed strap is
placed around the pipe and passed through the slot in
the metal body of the wrench. The strap is then pulled
up tight; and as the mechanic turns the wrench in the
desired direction, the webbed strap tightens further
around the pipe. This gripping action causes the pipe to
Many special nuts are made with notches cut into
their outer edge. For these nuts a hook spanner (fig.
1-40) is required. This wrench has a curved arm with a
lug or hook on the end. This lug fits into one of the
notches of the nut, and the handle is turned to loosen or
tighten the nut. This spanner may be made for just one
particular size of notched nut, or it may have a hinged
arm to adjust it to a range of sizes.
Another type of spanner is the pin spanner. Pin
spanners have a pin in place of a hook. This pin fits into
a hole in the outer part of the nut.
Face pin spanners are designed so that the pins fit
into holes in the face of the nut (fig. 1-40).
When you use a spanner wrench, you must make
sure the pins, lugs, or hooks make firm contact with the
nut while the turning force is transferred from the
wrench to the nut. If this is not done, damage will result
to tools or equipment or injury to personnel.
SETSCREW WRENCHES (ALLEN AND
In some places it is desirable to use recessed heads
on setscrews and capscrews. One type of screw (Allen)
is used extensively on office machines and in machine
shops. The other type (Bristol) is used infrequently.
Recessed-head screws usually have a hex-shaped
(six-sided) recess. To remove or tighten this type of
screw requires a special wrench that will fit in the
recess. This wrench is called an Allen-type wrench.
Allen wrenches are made from hexagonal L-shaped
Figure 1-39.Strap wrench.
Figure 1-40.General-purpose spanner wrenches.