The inside /upper/lower caliper

The inside calipers are used to measure the internal size of an object.
The upper caliper requires manual adjustment prior to fitting , fine setting of this caliper type is performed by tapping the caliper legs lightly on a handy surface until they will almost pass over the object . A light push against the resistance of the central pivot screw then spreads the legs to the correct dimension and provides the required , consistent feel that ensures a repeatable measurement.
The lower caliperhas an adjusting screw that permits it to be carefully adjusted without removal of the tool from the workpiece.