(6) Staybolt taps. Staybolt taps (fig 30) are used principally in boiler
locomotive and railroad shops for tapping the staybolt holes in the outer and inner
plates or shells of boilers.
(7) Mud or washout taps. Mud or washout taps (fig 30) have 6 flutes with a
1-1/4-inch taper per foot and 12 threads per inch. They are used to cut special
American National or V-form threads when tapping mud plug drain holes.
(8) Fusible plug tap. The fusible plug tap (not illustrated) is made of
carbon steel and has a 1-1/4-inch taper per foot. It has a thread length of 4-3/8
inches, is 1-inch square on the shank, has 4 flutes, and is 7 inches long.
(9) Pipe tap and drill. A pipe tap and drill (not-illustrated) is a
combination twist drill and tap. The tap portion follows the twist drill tip. The
tool does drilling and tapping in one operation. They are made of carbon steel
with a tapered square shank and sized to drill and tap holes 1/4--18, 3/8--18, and
1/2--14.
c. Types of dies. Dies are made in several different shapes and are of the
solid or adjustable type.
(1) Solid dies.
(a) Square pipe dies. The square pipe die (fig 31) will cut American
Standard Pipe Thread only. It is issued in sizes that will cut threads on pipe
from 1/8--27 to 3-8.
(b) Rethreading dies. A rethreading die (fig 31) is used principally for
dressing over bruised or rusty threads on screws and bolts. However, it may be
used for cutting occasional new threads. It is available in a variety of sizes for
rethreading American Standard Coarse and Fine threads. These dies are usually
hexagon in shape and can be turned with a socket, box, open-end, or any wrench that
will fit. Rethreading dies are available in sets of 6, 10, 14, and 28 assorted
sizes in a case.
Figure 31.
Types of solid dies.
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