Centralab (CRL) R2-52 Fastatch Rear Dual Volume Control Type B, Taper C2, outer shaft measures 3/4 round  diameter 1/4 inch flat, top portion of shaft measures 1 3/8 inches and second section of outer shaft diameter (quarter way from bottom measures 1/4 inch round, bottom section of shaft measures 1 inch; control base diameter measures 15/16 inches (7/8") by overall shaft length measures 2 3/8 inches long.