For transferring and comparing distances, dividers are commonly used. They are classified according to the style of joint and the length of the leg. The most simple joint is the friction and, like all frictional devices, is hard to set accurately. Lock-joint dividers can be moved freely to approximately the right position, the joint locked, and the adjusting screw used for the final setting.
Wing dividers, Fig. 13, are of about the same construction as the lock joint, except that the fastening is made on the wing instead of at the pivot. The best of all forms has a spring adjustment as shown in Fig. 14. In this type, a spring tends to open the dividers, and the legs are closed against the spring by a nut working on a screw which is fastened to one leg and passes freely through the other. The length of dividers varies from 21/2 to 10 inches.
The distance to which dividers can be opened is generally about equal to the length of the leg. For distances above 10 inches, trammel points, Fig. 15, are convenient. They consist of hardened steel points attached to metal sockets and can be used on rods of any length. One point may have a spring adjustment and, in that case, can be set in the same manner as a pair of wing dividers.
Fig. 13. Wing Dividers.
Fig. 14. Tool-Makers' Dividers.
Courtesy of Brown and Sharpe Manufacturing Company, Providence, Rhode Island.