55 tooth, metal gearApproximate measurments: Outside diameter (tip of tooth to tip of tooth) = 5/16"Insert's shaft diameter = 1& 1/2", with one 3/16" by 3/8" keyShaft diameter of the gear if the insert were removed is 2& 1/2", with one 1/2" by 1/4" keyWidth of gear = 1& 1/4"Mr. Gears Inc, 2149-2129 Rev D