To get the best grinding effect, you should use the No. 1 quality grinding cups(grinding pins) made by SANSUNG company.
Sansung makes and supplies 4 models of grinding cups(grinding pins) as below:
wing(shoulder drive), with 8mm shank/shaft.
san-drive, with 9mm shank/shaft
round/spherical ballistic water way
for steel removal
Note: when using grinding machine with a collect chuck, the O-ring must be removed.