with a lead pencil. To obtain the slant of the thread,
lines 8 and 9 are drawn, and from these line 10, touching 8 and 9 where
they meet lines 2 and 5; the threads may then be drawn in from the arcs
as 6, 7, etc. The side of the thread will show at the top and the bottom
as at A B, because of the coarse pitch and the thread on the other or
unseen side of the bolt slants, as denoted by the lines 12, 13; and
hence to draw the sides A B, the triangle must be set from one thread to
the next on the opposite side of the bolt, as denoted by the dotted
lines 12 and 13.

[Illustration: Fig. 211.]

If the curves of the thread are to be drawn in, they may be obtained as
in Figure 211, which is substantially the same as described for a V
thread. The curves _f_, representing the sides of the thread, terminate
at the centre line _g_, and the curves _e_ are equidistant with the
curves _c_ from the vertical lines _d_. As the curves _f_ above the
line are the same as _f_ below the line, the template for _f_ need not
be made to extend the whole distance across, but one-half only; as is
shown by the dotted curve _g_, in the construction for finding the curve
for square-threaded nuts in Figure 212.

[Illustration: Fig. 212.]

[Illustration: Fig. 213.]

A specimen of the form of template for drawing these curves is shown in
Figure 213; _g_ _g_, is the centre line parallel to the edges R, S;
lines _m_, _n_, represent the diameter of the thread at the top, and
_o_, _p_, that at the bottom or root; edge _a_ is formed to the points
(found by the constructions in the figures as already explained) for the
tops of the thread, and edge _f_ is so formed for the curve at the
thread bottoms. The edge, as S or R, is laid against the square-blade to
steady it while drawing in the curves. It may be noted, however, that
since the curve is the same below the centre line as it is above, the
template may be made to serve for one-half the thread diameter, as at
_f_, where it is made from _o_ to _g_, only being turned upside down to
draw the other half of the curve; the notches cut out at _x_, _x_, are
merely to let the pencil-lines in the drawing show plainly when setting
the template.

When the thread of a nut is shown in section, it slants in the opposite
direction to that which appears on the bolt-thread, because it shows the
thread that fits to the opposite side of the bolt, which, therefore,
slants in the opposite direction, as shown by the lines