All of our stainless steel torque arms are currently laser cut in Australia and assembled and finished. We use thick 6mm stainless steel plate with anti-rotation slot and nylon lock nuts stainless steel fasteners as well.
Torque arms are used to prevent axle rotation in hub motors. When a hub motor is powered up running, for all the torque that the motor generates spinning a wheel forwards, there is an equal and opposite torque on the axle causing it to rotate backwards "Newton's Third Law ".
In most electric bicycle hub motors, the axle is machined with flats on either side which key into the dropout slot and provide some measure of support against rotation. In many cases this is sufficient.
However, in high power systems 500 watts and upwards it will generate a lot of torque, or in setups with weak dropouts, the forces present can exceed the material strength and pry the dropout open. When that happens, the axle will spin freely, wrapping and severing off the motor cables and potentially causing the wheel to fall right out of the bike.
Rear Torque Arm:
6 mm Thick
Suit 10mm Hub Motor Axle.