I noted this with some wheels. The I.D. seems to vary between some manufacturers. Likely, an issue with conversion between metric and imperial measurements?Just recieved a grinding wheel . . .Bore measures .916" . . .oversize for the nominal "7/8'" (.875).
I tried shimming the arbor for one with tape, but also got a lot of vibration.
Better to stick with brands that you know will fit.
Philbert