A Pair of EBike Torque Arm. Size M12 fits all kind of motors on www.bmsbattery.com except MagicPie3 motor and Q11 motor . Size M14 fits MagicPie3 motor and Q11 motor . The function is to reinforce the front fork and rear drop out. Size M12 is for 12mm axle. Size M14 is for 14mm axle.