The Scorpion HK-2221 motors are built with 4mm hardened steel shafts that will last through countless hours of flying fun, but occasionally, on a "Less than Perfect" landing, you may bend or break one. For these occasions, we offer factory replacement shafts for all the HK-22mm Scorpion Motors. The shaft for the HK-2221 series motors measures 4mm in diameter, and is 58.7mm in long. The pinion end of this shaft is ground down to 3.17 mm. The shafts can be cut shorter with a Dremel tool and a cut-off wheel if necessary to fit other motors. Note: The shafts in the Scorpion motors are a slight press fit into the aluminum front housing. The shafts will not just slide out when the setscrews are removed. They need to be pressed out in a bearing press, or in a drill press, with the front housing of the motor supported in a block of wood to prevent warping the front housing. Weight including packaging 6.1g