been used. Both the taper and plug taps should pre-
cede the use of the bottoming hand tap.
Pipe taps are used for pipe fittings and other
places where extremely tight fits are necessary. The
tap diameter, from end to end of the threaded portion,
increases at the rate of 3/4 inch per foot. All the
threads on this tap do the cutting, as compared to the
straight taps where only the nonchamfered portion
does the cutting.
Dies are made in several different shapes and are
of the solid or adjustable type. The square pipe die
(fig. 2-10) will cut American Standard pipe thread
Figure 2-10.Types of solid dies.
only. It comes in a variety of sizes for cutting threads
on pipe with diameters of 1/8 inch to 2 inches.
A rethreading die (fig. 2-10) is used principally for
dressing over bruised or rusty threads on screws or
bolts. 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.
Round split adjustable dies (fig. 2-11) are called
button dies and can be used in either hand diestocks
or machine holders. The adjustment in the screw ad-
justing type is made by a fine-pitch screw that forces
the sides of the die apart or allows them to spring
together. The adjustment in the open adjusting types
is made by three screws in the holder, one for expand-
ing and two for compressing the dies. Round split
adjustable dies are available in a variety of sizes to cut
American Standard coarse and fine threads, special
form threads, and the standard sizes of threads that are
used in Britain and other European countries. For
hand threading, these dies are held in diestocks
(fig. 2-12). One type of diestock has three pointed
screws that will hold round dies of any construction,
Figure 2-11.Types of adjustable