Thread cutting is more accurately and economically done by machine, but necessity frequently arises for cutting threads by hand. Taps and dies for hand work are made in many forms and sizes, of various standards of threads. They are usually made for cutting right-handed threads, as left-handed threads are used only for some particular requirement.

Fig. 209 shows a common type of machinists' hand taps for threading nuts. No. 1 is a taper tap, which may be used to ream out a hole and start the cutting of threads gradually, distributing the wear along the tap. No. 2 is a plug tap used for quicker cutting than No. 1. No. 3 is a bottoming tap used after No. 2 for cutting threads to the bottom of a hole.

A convenient form of die for bolt threading by hand is that shown in Fig. 210. This consists of a holder, made up of several parts, and four cutters. An extra set of cutters, or " chasers," is shown beside the die. These cutters may be adjusted to suit rods varying about 1/32-inch in diameter and may be readily removed for renewing. Fig. 211 shows a die-stoek A used for holding and turning the die, and an adjustable tap wrench B for turning the taps of Figs. 209.

Fig. 209. - Taps.

Fig. 210. - Threading Dies.

Fig. 211. - Die Stock and Tap Wrench.

All taps and dies are marked with the diameter of bolt and nut they will cut, the number of threads per inch, and the class or standard to which the thread belongs.

Fig. 212. - Forms of Wrenches.