To give a sense of the magnitude of the forces, a hub motor with a 12mm axle making 40 N-m of torque will exert a spreading force of slightly below 1000lb on each dropout. A torque arm is definitely a separate piece of metal mounted on the axle that may have this axle torque and transfer it even more up the frame, as a result relieving the dropout itself from currently taking all the stresses.
Tighten the 1/4″ bolt between your axle plate and the arm as snug as possible. If this nut is loose, after that axle can rotate some quantity and the bolt will slide in the slot. Though it is going to bottom out preventing further rotation, by enough time this 
occurs your dropout may already be damaged.
The tolerances on electric motor axles can vary 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 tiny amount of filing could be essential for the plate to slide on. In situations where in fact the axle flats happen to be a lttle bit narrower than 10mm and you feel play, it isn’t much of an issue, nevertheless, you can “preload” the axle plate in a clockwise course as you tighten everything up.
Many Torque Arm china dropouts have quick release “lawyer lips” which come out sideways and stop the torque plate from sitting down flat against the dropout. If this is actually the case, you should be sure to get a washer that fits inside the lip spot. We make custom “spacer ‘C’ washer” because of this job, though the lock washer that comes with a large number of hub motors is normally about the proper width and diameter.
For the hose-clamp version, a small length of heat-shrink tubing over the stainless steel band can produce the ultimate installation look even more discrete and protect the paint job from getting scratched. We include several pieces of shrink tube with each torque arm program.
However, in high power devices that generate a lot of torque, or in setups with weak dropouts, the forces present can exceed the material durability and pry the dropout open. When that happens, the axle will spin freely, wrapping and severing off the engine cables and potentially leading to the wheel to fall correct 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 provide some way of measuring support against rotation. In many cases this is sufficient.