To give a sense of the magnitude of the forces, a hub engine with a 12mm axle producing 40 N-m of torque will exert a spreading force of slightly below 1000lb on every dropout. A torque arm is another piece of metal mounted on the axle which can have this axle torque and transfer it additional up the frame, therefore relieving the dropout itself from bringing each of the stresses.
Tighten the 1/4″ bolt between your axle plate and the arm as snug as possible. If this nut can be loose, after that axle can rotate some amount and the bolt will slide in the slot. Though it is going to bottom out and prevent further rotation, by the time this occurs your dropout may already be damaged.
The tolerances on engine axles can vary from the nominal 10mm. The plate may slide on freely with a little of play, it could go on properly snug, or sometimes a little amount of filing could be essential for the plate to slide on. In situations where in fact the axle flats are a bit narrower than 10mm and you feel play, it is not much of an issue, nevertheless, you can “preload” the axle plate in a clockwise direction as you tighten everything up.
Many dropouts have quick release “lawyer lips” that come out sideways and stop the torque plate from seated toned against the dropout. If this is the case, you will need to be sure to get a washer that suits inside the lip region. We make custom “spacer ‘C’ washer” because of this job, although lock washer that is included with various hub motors can often be about the proper width and diameter.
For the hose-clamp unit, a small amount of heat-shrink tubing over the stainless steel band can help to make the final installation look even more discrete and Torque Arm china protect the paint job from getting scratched. We involve several bits of shrink tube with each torque arm offer.

However, in high electricity devices 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 creating the wheel to fall proper out of your bike.

In most electric 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.