The other type (Bristol) is used
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
bars of tool steel (fig. 1-17). They generally range in
size up to 3/4 inch.
When using the Allen-type
wrench, make sure you use the correct size to prevent
rounding or spreading the head of the screw. A snug
fit within the recessed head of the screw is an
indication that you have the correct size.
The Bristol wrench is made from round stock. It
is also L-shaped, but one end is fluted to fit the flutes
or little splines in the Bristol setscrew (fig. 1-17).
SAFETY RULES FOR WRENCHES
There are a few basic rules that you should keep
in mind when using wrenches. They are as follows:
Always use a wrench that fits the nut
Keep wrenches clean and free from oil.
Otherwise they may slip, resulting in possible serious
injury to you or damage to the work.
Do not increase the leverage of a wrench by
placing a pipe over the handle. Increased leverage
may damage the wrench or the work.
Provide some sort of kit or case for all
wrenches. Return them to the case at the completion
of each job. This saves time and trouble and aids
selection of tools for the next job. Most important, it
eliminates the possibility of leaving them where they
can cause injury to personnel or damage to equipment.
Determine which way a nut should be turned
before trying to loosen it. Most nuts are turned
counterclockwise for removal.
This may seem
obvious, but even experienced people have been
observed straining at the wrench in the tightening
direction when they wanted to loosen the nut.
Learn to select your wrenches to fit the type
of work you are doing. If you are not familiar with
these wrenches, make arrangements to visit a shop
that has most of them, and get acquainted.
Figure 1-17.-Allen- and Bristol-type wrenches.
Many types of metal-cutting tools are used by
skilled mechanics of all ratings. As you become
better acquainted with the ABE rating, you will
probably discover many tools that you use for cutting
metal that are not described in this text. In this text,
only the basic hand metal-cutting tools will be
SNIPS AND SHEARS
Snips and shears are used for cutting sheet metal
and steel of various thicknesses and shapes.
Normally, the heavier or thicker materials are cut by
One of the handiest tools for cutting light (up to
1/16-inch thick) sheet metal is the hand snip (tip
The STRAIGHT HAND SNIPS, shown in
figure 1-18, have blades that are straight and cutting
edges that are sharpened to an 85-degree angle. Snips
like this can be obtained in different sizes, ranging
from the small, 6-inch, to the large, 14-inch, snip. Tin
snips will also work on slightly heavier gauges of soft
metals, such as aluminum alloys.
Snips will not remove any metal when a cut is
made. There is danger, though, of causing minute
metal fractures along the edges of the metal during the
shearing process. For this reason, it is better to cut
just outside the layout line. This procedure will allow
you to dress the cutting edge while keeping material
within required dimensions.
Cutting extremely heavy gauge metal always
presents the possibility of springing the blades. Once
the blades are sprung, hand snips are useless. When