Outside callipers are used for measuring work pieces or checking or transferring measurements. They are particularly useful for checking external diameters or testing outside edges such or opposite faces for parallel. With careful application, they can be accurate to 0.5mm. Their overall accuracy is dependent on fine feel between the calliper points and the workpiece. Callipers should be held lightly, contacting workpieces lightly and without excessive force. The callipers are available in either spring or firm joint.
Similar to dividers, spring callipers are typically constructed from two lengths (or legs) of curved steel that taper to a fine point to form an arc on either side of the calliper. The wider end is fitted with a loop of spring steel and a peg to help pivot the scribe on one leg. The distance between the leg points is adjusted by a screw and nut that is positioned one quarter to half way down the legs. The screw also helps keep the legs in place.

Firm point callipers keep their setting by friction between the legs at the fixed end. They can be adjusted with the application of light finger pressure or gentle taps.