Martin stock miter gears are manufactured from 0.4 carbon steel. The \"M\" series is furnished unhardened with plain bore. The \"HM\" series is furnished hardened teeth with plain bore. The \"HMK\" series is furnished hardened teeth with keyway and setscrew for installation on the shaft. Hardened miter gears have approximately 50% more horsepower capacity and provide greater gear wear than untreated gears. All Martin miter gears are cut with the 20 deg pressure angle system. Martin Straight Tooth Miter Gear, Bored-to-Size, Series: HMK, 1-1/2 to 1-1/2 in Bore Dia, 4.236 in Outside Dia, 24 Teeth, 6 Diametral Pitch, 4 in, 0.86 in Face Width, Hub with Set Screw, 3 in Hub Dia, 1.313 in Hub Projection, 2-5/16 in Overall Length, 20 deg Pressure Angle, 3/8 x 3/16 in Keyway, Steel