Easy to adjust for accurate measurement. Professional precision tool set Handles are rigidly attached to contact pistons and are automatically self-centering Rigid double-action handle with self-centering feature for checking fast through holes, slots and recesses up to 6" deep Ends of both contacts are head treated stainless steel and precision ground to a radius to allow proper clearance on the smallest hole the pressure gauge will go into. 6pcs gauge set: 5/16" - 6" (8mm - 150mm): Gauges 8-12.7, 12.7-19, 19-32, 32-54, 54-90 and 90-150mm Specification: Material: Hardened tool steel Color: Silver Range: 5/16" - 1/2", (8 - 12.7mm) 1/2" - 3/4", (12.7 - 19mm) 3/4" - 1-1/4", (19 - 32mm) 1-1/4" - 2-1/8", (32-54mm) 2-1/8" - 3-1/2", (54 - 90mm) 3-1/ 2" - 6" (90 - 152mm) Purpose: Under uniform spring tension, the gauge piston expands from center to hole diameter or width of the slot to be measured, then locked in place with a knurled knob. Hole size is determined by measuring the contact point using micrometer or caliper. Package included: 6pcs x Precision Telescopic Gage (packed with bag)