5/8-11 spindle. With 7/8 arbor adapter. Model 6559. Grinding wheel fits okay works okay top of picture. But the pack of cutting wheel center hole is too big. Tried it wouldn't cut. Maybe the grinder does not use cutting wheels for metal. Or I purchased the wrong wheels?

Never mind I figure it out. You put the two flat washers on first
Before the spindle. That give the thin cut off disk the rooms it needs
To rotate