To give a feeling of the magnitude of these forces, a hub electric motor with a 12mm axle generating 40 N-m of torque will exert a spreading force of slightly below 1000lb on every single dropout. A torque arm is certainly another piece of metal attached to the axle which can consider this axle torque and transfer it additional up the frame, therefore relieving the dropout itself from taking all of the stresses.
Tighten the 1/4″ bolt between the axle plate and the arm as snug as possible. If this nut is certainly loose, in that case axle can rotate some volume 
and the bolt will slide in the slot. Though it will eventually bottom out and stop further rotation, by the time this happens your dropout may Torque Arm china previously be damaged.
The tolerances on motor axles may differ from the nominal 10mm. The plate may slide on freely with a lttle bit of play, it may go on flawlessly snug, or sometimes a small amount of filing may be essential for the plate to slide on. In conditions where the axle flats will be a bit narrower than 10mm and you are feeling play, it is not much of a concern, nevertheless, you can “preload” the axle plate in a clockwise path as you tighten everything up.
Many dropouts have quick release “lawyer lips” that come out sideways and prevent the torque plate from sitting toned against the dropout. If this is the case, you will need to be sure to have a washer that matches inside the lip location. We make custom “spacer ‘C’ washer” for this job, although lock washer that is included with various hub motors can often be about the right width and diameter.
For the hose-clamp style, a small amount of heat-shrink tubing over the stainless band can generate the final installation look more discrete and protect the paint job from getting scratched. We incorporate several bits of shrink tube with each torque arm package deal.
However, in high electric power systems that generate a whole lot of torque, or in setups with weak dropouts, the forces present can exceed the material durability and pry the dropout open. When that occurs, the axle will spin freely, wrapping and severing off the electric motor cables and potentially triggering the wheel to fall proper out of your bike.
In most electrical bicycle hub motors, the axle is machined with flats on either side which key into the dropout slot and offer some way of measuring support against rotation. In many cases this is sufficient.