This Oregon 4 1/8in. diameter grinding wheel leaves a precision finish on saw chain and work with our Oregon Mini Grinders Item#s 193061 and 19301. Single grinding wheel included. Bore Diameter (in.): 7/8, Chain Pitch (in.): 4/4, .325, and mini 3/8, Rated RPM: 9,300, Product Type: Grinding wheel, Wheel Diameter (in.): 4 1/8