plate punched, or should do so in all carefully executed work, for it
is easy to understand that the die which might give a suitable taper
in a three-fourths inch plate would give too great a taper in a
three-eighths inch plate. There is no fixed rule; practical experience
determines this in a rough and ready way--often a very rough way,
indeed, for if a machine has to punch different thicknesses of plate
for the same size of rivets, the workman will seldom take the trouble
to change the die with every variation of thickness. The maker of
punches and dies generally allows about three sixty-fourths or 0.0468
of an inch clearance.

The following formula is also used by punch and die makers:

Clearance = D = d + 0.2t

where
D = diameter of hole in die block;
d = diameter of cutting edge of punch;
t = thickness of plate in fractions of an inch;

that is to say, the diameter of the die hole equals diameter of punch
plus two-tenths the thickness of the plate to be punched.

_Example_.--Given a plate 3/8 or 0.375 of an inch thick, the diameter
of the punch being 13/16 or 0.8125 of an inch, then the diameter of
the die hole will be as follows:

Diameter of die hole = 0.8125 + 0.375 X 0.2 = 0.8875 inch diameter,
or say 7/8 or 0.875 inch diameter.