1/4in Shank.

By changing the bearing the size of the rebate can be altered.
Supplied with four bearings.
19 mm Bearing gives rebate of 7.9 mm
16 mm Diameter gives rebate of 9.5 mm
12.7 mm Diameter gives rebate of 11.1 mm
9.5 mm Diameter gives rebate of 13.7 mm
D = 35 mm
C = 12.7 mm