Starrett 579A Self Centering Telescoping Gauge With 2 Telescoping Arm, 5/16" - 1/2" Range, 2-3/8" Handle Length

It has a slightly greater range and two telescoping contacts in comparison with no. 229 series

Handle is rigidly attached to the contact plungers and is automatically self-centering

Constant spring tension gives uniform contact pressure

Both plungers are easily locked at any desired setting

Telescoping gauge is used for determining the true size of holes, slots, and recesses up to 6". The ends of both contact is hardened and ground to a radius to allow proper clearance on the smallest hole the gauge will enter. This tool must be slightly "rocked" in the hole being measured to ensure that the tool is on the proper diameter before it is locked and withdrawn. The final hole size is obtained by measuring over the gauge contact with a micrometer.
Brand: Starrett, Model: 579A