THE THREADING SET WITH RECTANGULAR
ADJUSTABLE DIES, DIESTOCK,
WRENCH, GUIDES AND TAPS.
BOLT AND SCREW THREADING SET WITH
ROUND ADJUSTABLE SPLIT DIES,
DIESTOCKS, TAPS, TAP WRENCHES,
d. Use of taps.
(1) Selecting a tap drill. The size of a tap is the outside diameter of
its threads; therefore, theoretically the hole drilled for tapping could be smaller
than the tap by twice the depth of the thread if a full thread is cut. The shape
of the thread partly determines the amount to be subtracted from the tap diameter.
Do not use a tap drill that is too small in diameter, as this will cause tapping
troubles. A drilled hole should be of sufficient diameter to produce a thread
depth of approximately 75 percent. This 75 percent is only an average. Actually,
the percentage may vary from 50 to 53 percent for small or deep holes to a maximum
of 83 percent on any size. A definite thread depth for all sizes, under all
conditions, is not practical. You must determine which is most suitable by
analyzing the following conditions: diameter of tapped hole, nature of material
being tapped, depth of tapped hole, and the pitch.