To give a sense 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 just under 1000lb on every dropout. A torque arm can be another piece of metal attached to the axle that may take this axle torque and transfer it further up the frame, hence relieving the dropout itself from choosing all the stresses.
Tighten the 1/4″ bolt between your axle plate and the arm as snug as possible. If this nut is definitely loose, after that axle can rotate some sum and the bolt will slide in the slot. Though it is going to bottom out and stop further rotation, by enough time this happens your dropout may already be damaged.
The tolerances on engine axles may differ from the nominal 10mm. The plate may slide on freely with a bit of play, it could go on correctly snug, or sometimes a small amount of filing may be essential for the plate to slide on. In circumstances where in fact the axle flats will be somewhat narrower than 10mm and you feel play, it isn’t much of a concern, nevertheless, you can “preload” the axle plate in a clockwise route as you tighten everything up.
Many dropouts have speedy release “lawyer lips” that come out sideways and stop the torque plate from resting toned against the dropout. If this is actually the case, you will want to be sure to possess a washer that suits inside the lip spot. We make customized “spacer ‘C’ washer” because of this job, although lock washer that comes with many hub motors 
is often about the proper width and diameter.
For the hose-clamp style, a small amount of heat-shrink tubing over the stainless band can produce the final installation look even more discrete and protect the paint job from getting scratched. We incorporate several bits of shrink tube with each torque arm Torque Arm china package deal.
However, in high electric power devices that generate a lot of torque, or in setups with weak dropouts, the forces present can exceed the material power and pry the dropout open. When that occurs, the axle will spin freely, wrapping and severing off the motor cables and potentially leading to the wheel to fall correct out from the 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 measure of support against rotation. In many cases this is sufficient.