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 78293 3" Dia. x 2S Fine, Type R Unitized Locking-Type Disc, 25/pack
3M 02140, Fibre Disc Backup Pad, TN Quick Change , 4-1/2 in x 5/8-11 Internal, 7000045746
Dynabrade 78586 1/4" Dia. x 1-1/2" W x 1/8" Center Hole, 180 Grit, 100/pack
Norton 66623335427, 2" Dia Vortex Rapid Prep Quick-Change Non-Woven Abrasive Disc, Medium Grade, 50 Each
Dynabrade 78182 3" Dia. Medium DynaBrite Locking-Type Disc, 25/pack
3M 37024, Extra Large Drywall Sanding Sponge 910-DDA, Dual Angle, 2-1/2 in x 8 in x 1 in, Fine, 7010375249 
