M4 shafts are used on medium tractor winches, small wood chippers, small rototillers and hay rakes. Transmittable HP at 540 rpm is 35 HP, at 1000 rpm is 55 HPM4 SP-33 Shear pin on one end. Six spline 1 3/8" ends. Min length: 33" Max length: 46" 25 lb.