Types of common taps

Figure 1-38.-Types of common taps. Plug hand taps have a chamfer length of 3 to 5 threads and are designed for use after the taper tap. Bottoming hand taps are used for threading the bottom of a blind hole. They have a very short chamfer length of only 1 to 1 1/2 threads for this purpose. This tap is always used after the plug tap has been used. Both the taper and plug taps should precede 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. 1-39) will cut American Standard Pipe thread Figure 1-39.-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. 1-39) 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. 1-40) are called “Burton” dies and can be used in either hand diestocks or machine holders. The adjustment in the screw adjusting type is made by a fine-pitch screw, which forces the sides of the die apart or allows them to spring together. The adjustment in the open adjusting type is made by means of three screws in the holder, one for expanding and two for compressing the dies. Two piece collet dies (fig. 1-40) are used with a collet cap (fig. 1-41) and collet guide. The die halves are placed in the cap slot and are held in place by the guide, which screws into the underside of the cap. The die is adjusted by setscrews at both ends of the interval slot. This type of adjustable die is issued in various sizes to cover the cutting ranges of American Standard Coarse and Fine and special-form threads. Diestocks to hold the dies come in three different sizes. Two-piece rectangular pipe dies (fig. 1-40) are available to cut American Standard Pipe threads. They are held in ordinary or ratchet-type diestocks (fig. 1-42). Threading sets are available in many different combinations of taps and dies, together with diestocks, tap wrenches, guides, and necessary screwdrivers and 1-24