TM 9-243
TYPES AND USES
Taps and dies are used to cut threads in metal, plastics
or hard rubber. The taps are used for cutting internal
threads, and the dies are used to cut external threads.
TAPS
Taps are made of hardened steel and have the following
parts: a square end (1) a round shank (2) a body
(threaded) section (3) and a chamfer (4). The square
end is used to turn the tap with either a straight or
T-handled tap wrench. The shank is a smooth, rounded
section which is immediately behind the threaded sec-
tion. The body (threaded) section contains four flutes
which have threads cut into their upper edges. They
have a hollow section near the center to permit metal
shavings to fall away from the cutting edges. The
chamfer is the non-threaded end of the tap. It allows the
tap to be positioned squarely in the metal to be threaded
without engaging the threads of the tap.
TAPER (STARTING) HAND TAP
The taper (starting) hand tap has a chamfer (non-
threaded) length equal to eight to ten threads. The taper
hand tap is used to start tapping operations.
BOTTOMING HAND TAP
The bottoming hand tap has a chamfer length equal to
one to one and one-half threads. This tap is used for
threading the bottom of a blind hole only after the taper
and plug taps have been used.
This tap is also used when tapping hard materials.
PLUG/PIPE HAND TAP
The pipe tap has a tapered diameterwhich increases at
a rate of 3/4 inch per foot. All the threads on the pipe tap
are designed to cut pipe. The pipe tap is used for cutting
pipe fittings and in other places where extremely tight
fits are required.
BOILER HAND TAPS
There are two types of boiler taps, straight and tapered.
Straight boiler taps range in size from 1/2 inch to 1-1/2
inches in diameter and have a chamfer for starting the
tap.
Tapered boiler taps have tapered diameters which
increase at a rate of 3/4 inch per foot.
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