Accuracy: ?2″.
To inspect protractor, taper gage, index plate, index head and goniometer, can also be used to set angle.
Made of special alloy steel, hardness HRC64, high stability, wear resistance and easy combination.
Can be combined to any angle with interval 6 seconds after combination (6″, 12″, 18″, … , 360?).

Dynabrade 78594 3/8" Dia. x 1-1/2" W x 1/8" Center Hole, 60 Grit, 100/pack
3M 26116, PPS Series 2.0 Adapter, Type S25, 1/4 Female, 19 Thread BSP, 7100135957
3M 26053, PPS Series 2.0 Adapter, Type S14, 7/16 Male, 14 Thread UNC, 7100135932
3M 26138, PPS Series 2.0 Adapter, Type S42, 3/8 Female R-Angle, 19Thread BSP, 7100135930 
