To give a feeling of the magnitude of the forces, a hub electric motor with a 12mm axle making 40 N-m of torque will exert a spreading force of just under 1000lb on every dropout. A torque arm is certainly a separate piece of metal mounted on the axle that may have this axle torque and transfer it even more up the frame, hence relieving the dropout itself from currently taking all of the stresses.
Tighten the 1/4″ bolt between your axle plate and the arm as snug as possible. If this nut is usually loose, then axle can rotate some volume and the bolt will slide in the slot. Though it is going to bottom out and prevent further rotation, by enough time this occurs your dropout may previously be damaged.
The tolerances on motor axles may differ from the nominal 10mm. The plate may slide on freely with somewhat of play, it could go on properly 
snug, or in some cases 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 prevent the torque plate from seated smooth against the dropout. If this is the case, you will need to be sure to get a washer that meets inside the lip region. We make custom “spacer ‘C’ washer” for this job, although lock washer that is included with many hub motors is normally about the right width and diameter.
For the hose-clamp model, a small amount of heat-shrink tubing over the stainless band can produce the final installation look 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 systems 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 happens, the axle will spin freely, wrapping and severing off the motor cables and potentially causing 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 in to the dropout slot and offer some way of measuring support against rotation. In many cases this is sufficient.
