ut would advance in one turn, and it should not be confused with the
pitch _p_, which is the distance between the centers of adjacent
threads. Obviously the lead and pitch of a single thread are the same.)

=Cutting a U. S. Standard Thread.=--The method of cutting a U. S.
standard thread is the same as described for a V-thread, so far as
handling the lathe is concerned. The thread tool must correspond, of
course, to the shape of a U. S. standard thread. This tool is first
ground to an angle of 60 degrees, as it would be for cutting a V-thread,
and then the point is made flat as shown in Fig. 9. As will be recalled,
the width of this flat should be equal to 1/8 of the pitch. By using a
gage like the one shown at _G_, the tool can easily be ground for any
pitch, as the notches around the periphery of the gage are marked for
different pitches and the tool-point is fitted into the notch
corresponding to the pitch wanted. If such a gage is not available, the
width of the flat at the point can be tested by using, as a gage, a U.
S. standard tap of the same pitch as the thread to be cut.

When cutting the thread, the tool is set square with the blank, and a
number of successive cuts are taken, the tool being fed in until the
width w of the flat at the top of the thread is equal to the width at
the bottom. The thread will then be the right size provided the outside
diameter _D_ is correct and the tool is of the correct form. As it would
be difficult to measure the width of this flat accurately, the thread
can be tested by screwing a standard nut over it if a standard thread is
being cut. If it is being fitted to a tapped hole, the tap itself is a
very convenient gage to use, the method being to caliper the tap and
then compare its size with the work.

[Illustration: Fig. 9. U. S. Standard Thread, Thread Tool, and Gage]

A good method of cutting a U. S. standard thread to a given size is as
follows: First turn the outside of the blank accurately to diameter _D_,
and then turn a small part of the end to diameter _r_ of the thread at
the root. The finishing cut for the thread is then taken with the tool
point set to just graze diameter _r_. If ordinary calipers were set to
diameter _r_ and measurements taken in the thread groove, the size would
be incorrect owing to the angularity of the groove, which makes it
necessary to hold the calipers at an angle when measuring. To determine
the root diameter divide 1.299 by the number of