DECIMAL EQUIVALENTS OF DRILL SIZES FROM " TO No. 80

TAP DRILL SIZES FOR REGULAR THREADS

THESE sizes give an allowance above the bottom of thread on sizes to 2; varying respectively as follows: for "V" threads, .010 to 055 inch; for U. S. S. and Whitworth threads, 005 to 027 inch. These are found by adding to the size at bottom of thread, of the pitch for "V" threads, and of the pitch for U. S. S. and Whitworth, the pitch being equal to 1 inch divided by the number of threads per inch. In practice it is better to use a larger drill if the exact size called for cannot be had.

A very simple rule, which is good enough in many cases, is:
Subtract the pitch of one thread from the diameter of the tap.
A-inch tap 16-thread would be minus

100

=

10%

=

drill; a-inch

10 or 0.75. a g-inch drill will do -inch drill, which is a

tap, ten-thread, would be minus
65 or o 65, or a little over of an inch, so
nicely. With a 1-inch tap we have I
little large but leaves enough thread for most cases.

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TAP DRILLS

For Machine Screw Taps

THESE drills will give a thread full enough for all practical purposes. but not a full thread as this is very seldom required in practical work, Further data along this line will be found in the tables which follow.