Calipers, like dividers, are made in many different forms, with and without screw adjustment. Fig. 63 illustrates the screwadjusting wing calipers for outside measurements; and Fig. 64 the firm-joint outside calipers, used for the same purpose.

Inside calipers for taking inside dimensions and inside distances are shown in Fig. 65.

Fig. 63.

Fig. 64.

Fig. 65.

Fig. 66.

The adjustable inside calipers are illustrated in Fig. 66. Calipers are used for measuring the distances between points, external and internal, when a rule could not be used with accuracy.

They are indispensable to the wood turner for measuring the diameters of cylindrical forms and other work while being turned to required dimensions in the lathe. When used by the pattern maker, they may be applied while the wood is revolving, until it has been reduced almost to the required dimensions; after which, when the calipers are used, the lathe should be stopped, to prevent the surface from being marked by the points, and in order to obtain exact measurements.

The calipers should not be pushed or forced over the piece, but in passing over the finished cylinder, the points should touch it lightly without springing the legs of the calipers; otherwise the required dimensions cannot be obtained with accuracy.