To give a feeling of the magnitude of the forces, a hub engine with a 12mm axle creating 40 N-m of torque will exert a spreading force of just under 1000lb on every single dropout. A torque arm is another piece of metal attached to the axle which can take this axle torque and transfer it additional up the frame, therefore relieving the dropout itself from bringing all the stresses.
Tighten the 1/4″ bolt between your axle plate and the arm as snug as possible. If this nut is certainly loose, after that axle can rotate some volume and the bolt will slide in the slot. Though it will eventually bottom out and stop further rotation, by enough time this takes place your dropout may previously be damaged.
The tolerances on motor axles can vary from the nominal 10mm. The plate may slide on freely with somewhat of play, it could go on flawlessly snug, or sometimes a tiny amount of filing may be essential for the plate to slide on. In circumstances where the axle flats will be a little narrower than 10mm and you feel play, it is not much of an issue, but you can “preload” the axle plate in a clockwise course as you tighten everything up.
Many dropouts have quick release “lawyer lips” that come out sideways and stop the torque plate from seated smooth against the dropout. If this is the case, you should be sure to have a washer that meets inside the lip spot. We make customized “spacer ‘C’ washer” for this job, although lock washer that is included with many hub motors is normally about the proper width and diameter.
For the hose-clamp unit, a small length of heat-shrink tubing over the stainless steel band can make the ultimate 
installation look even more discrete and protect the paint job from getting scratched. We include several bits of shrink tube with each torque arm package.
However, in high power devices that generate a lot of torque, or in setups with weak dropouts, the forces present may 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 correct 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 provide some measure of support against rotation. Oftentimes this is sufficient.