CALIPERS (corrupted from ealibre: see CA LIBRE ) . All instrument for measuring the diameter or thickness of objects. If a pair of ordinary dividers be applied to an object so that the extreme points of the diverging legs em brace it. the distance between the points of the two legs will be the exact thickness of the object. and this distance caul be determined in the usual units of length by applying the points to a scale and reading off the space subtended by them. This is the simplest form of calipers. If the dividers have a graduated arc attached, so arranged that it records exactly the distance apart of the points of the legs, we then have a registering calipers. Calipers of this general form are made in a variety of shapes and with a variety of registering and adjusting devices for special purposes. Generally the legs. in of being straight like the legs of dividers, are curved so as to converge toward each other -at the ex treme points. Fig. 1 shows a form of calipers for rough measurements such as measuring the di ameter of rolled rods or the thickness of rolled plates. Fig. 2 shows a form of calipers, known as micrometer calipers, for very precise measure meats. The mechanical principle embodied in the construction is that of a screw in a fixed nut. An opening to receive the work to be measured is afforded by the backward movement of the screw, and the size of the opening is indicated by the graduations. The pitch of the screw, or distance between its threads, is forty to the inch in this particular calipers, and the graduations OD the barrel are forty to the inch and are figured 0, 1, 2, etc., at every fourth division. As these
graduations conform to the pitch of the screw, each division equals the longitudinal distance traversed by the screw in one complete revolu tion, and shows that the calipers has been opened or of an inch. The beveled edge of the thimble is graduated into twenty-five parts and is figured at every fifth division, 0, 5, 10, 15. 20, etc. Each division when coincident with the base-line of the divisions on the barrel indicates that the gauge-screw has made of a revolution and that the opening of the calipers has increased of or of an inch. Hence to read the calipers multiply the number of divisions visible on the scale of the barrel by 25, and add the number of divisions on the scale of the thimble from zero to the line coincident with the base-line of the graduations on the barrel. For example, as the calipers is set in the illustra tion, there are three whole divisions visible on the barrel. Slultiplying this number by 25 and adding 5, the number of divisions registered on the scale of the thimble, the result is •,-;;?, of an inch. There are also special forms of micrometer calipers for the accurate measurement of V threads on screws, bolt-. etc.. and calipers for measuring the depths and thickness of gear-teeth and other purposes. A common form of calipers, known as vernier calipers. is shown by Fi:!. 3.
(See VERNIER.) fee (1A CGES.