No. 657P Magnetic Base. 1 15/16 x 1 5/8 x 1 7/8" (50 x 40 x 48 mm). Push-button on/off switch for one-hand operation. Base has three precision ground, magnetic contact points. Grips horizontally, vertically, and upside down. V-step holds base to arbors, shafts Base has extra 1/4-20 tapped hole on one side for mounting post., Manufacturer: Starrett