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The design of vernier caliper gages

Caliper gages are made in different lengths, starting with a useful range of about 5 inches, and are available in lengths of uo to 48 inches, or, exceptionally, ever longer. The depth of the jaw also varies, although not in a linear relationship with measuring range.
The form of the jaws may be designed for measuring external surfaces only, or can be provided with features permitting internal measurements as well. Measurements on interal surfaces are made either by inside gaging jaw tips or directly, by knife dege auxiliary jaws that can pass each other along a common mating plane. When measuring inside distances with the jaw tios, the combined thickness of the two tips must be added to the indicated dimension, unless the beam has separate graduations for outside and inside measurements.
Vernier calipers intended for general applications are made with plain sides, usually equipped with internal locking springs, whereas for precision measurements the combination type slides are preferred. The latter slides have a sliding clam that can be locked in position and serves as the nut for a fine adjusting screw acting on the measuring slide.
Some caliper gages have a depth gage tongue. This feature has some usefuless for rapid measurements, although the precision of depth gaging by this means is not considered to be equivalent to measurements between the jaws of the same instrument.
The purpose of the locking screw on the slide is to maintain a fixed jaw opening for the sequential measurement of parts with the same nominal size, using the caliper as a snap gage. Calipers must not, however, be considered equicalent substitutes for snap gages, primarily because the setting accuracy of a vernier caliper is inferior to the gage maker tolerances to which snap gages are made. The locking screw should be on the top side of the slide in order to draw the slide against the lower edge of the beam. The end of the locking screw must not act directly on the beam, but should transmit the locking force through an appropriate insert strip.