Fig. 1414.
[Fig. 1414] represents a pair of inside calipers with an adjustment screw having a right-hand screw at a and a left-hand one at b, threaded into two nuts pivoted into the arms, so that by operating the screw the legs are opened or closed, and are locked in position, so that they cannot move from an accidental blow. But as the threads are apt to wear loose, it is preferable to provide a set screw to one of the nuts so as to take up the wear and produce sufficient friction to prevent looseness of the legs.
Fig. 1415.
Fig. 1416.
Calipers are sometimes made double, that is to say, the inside and the outside calipers are provided in the one tool, as in [Fig. 1415], which represents a pair of combined inside and outside calipers having a set screw at c to secure the legs together after the adjustment is made. The object of this form is to have the measuring points equidistant from the centre of the pivot a in [Fig. 1416], so that when the outside legs are set to the diameter of the work as at b, the inside ones will be set to measure a hole or bore of the same diameter as at c.
This, however, is not a desirable form for several reasons, among which are the following:—