Application This adapter kit contains all the items necessary to mount depressed center wheels with 7/8′′ center holes on to standard portable right angle or vertical shaft grinders. Adapter hubs are threaded for mounting on to standard 5/8′′-11 NCRH spindles. This adapter kit may be used with wheel thicknesses of 1/8′′ or 1/4′′. All depressed center wheels must use the proper adapters for securely mounting the wheel to the spindle.