To give a feeling of the magnitude of the forces, a hub motor 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 can be a separate piece of metal mounted on the axle which can have this axle torque and transfer it additional up the frame, as a result relieving the dropout itself from spending each of the stresses.
Tighten the 1/4″ bolt between the axle plate and the arm as snug as possible. If this nut is definitely loose, in that case 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 may go on flawlessly snug, or in some cases a tiny amount of filing could be essential for the plate to slide on. In scenarios where in fact the axle flats will be a lttle bit narrower than 10mm and you are feeling play, it isn’t much of an issue, but you can “preload” the axle plate in a clockwise course as you tighten everything up.
Many dropouts have speedy release “lawyer lips” which come out sideways and stop the torque plate from relaxing smooth against the dropout. If this is the case, you will want to be sure to get a washer that matches inside the lip spot. We make customized “spacer ‘C’ washer” because of this job, although lock washer that comes with various hub motors can often be about the right 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 ultimate installation look more discrete and protect the paint job from getting scratched. We involve several pieces of shrink tube with each torque arm offer.
However, in high electricity systems that generate a lot of torque, or in setups with weak dropouts, the forces present may exceed the material power and pry the dropout open. When that Torque Arm china happens, the axle will spin freely, wrapping and severing off the engine cables and potentially creating 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. Oftentimes this is sufficient.