Bore Gauge Set STO3S116

Under spring tension, the plungers expand from the center to the size of the hole being measured and are then locked in place by a knurled knob. Final hole size is obtained by measuring over the contacts with a micrometer or vernier caliper. Double action (self centering) for quick checking of inside measurements. Rigid handle with self centering feature. Contact point ends are hardened tool steel and precision ground on a radius of the smallest hole the gauge will enter.