Types of adjustable

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 2-8