use, and is employed solely for explaining to a customer what is
required when a pivot or jewel is found to be broken.


HOW LARGE SCREWS ARE MADE.

The screws which hold the plates in place should have heads about 3/8"
in diameter, to be in proportion to the scale on which the balance and
escape wheel are gotten up. There is much in the manner in which the
screw heads are finished as regards the elegance of such a model. A
perfectly flat head, no matter how highly polished, does not look well,
neither does a flattened conehead, like Fig. 35. The best head for this
purpose is a cupped head with chamfered edges, as shown at Fig. 34 in
vertical section. The center _b_ is ground and polished into a perfect
concave by means of a metal ball. The face, between the lines _a a_, is
polished dead flat, and the chamfered edge _a c_ finished a trifle
convex. The flat surface at _a_ is bright, but the concave _b_ and
chamfer at _c_ are beautifully blued. For a gilt-edged, double extra
head, the chamfer at _c_ can be "snailed," that is, ground with a
suitable lap before bluing, like the stem-wind wheels on some watches.

[Illustration: Fig. 34]

[Illustration: Fig. 35]


FANCY SCREWHEADS.

There are two easy methods of removing the blue from the flat part of
the screwhead at _a_. (1) Make a special holder for the screw in the end