We ran into an issue: this motor has a fixed axel.  It requires the installer (me) to drop the axel into the frame through a slot called the “dropout” and then clamp it on using a nut or quick release lever.   Unfortunately, my mountain bike requires the axel to slide through holes in the frame and into the hub.  There is no way to drop a fixed axel through the holes (basically it wouldn’t connect). I switched the hub motor to my road bike with rear droputs and it fit, including the disk brake. Later, we switched the motor to the 700 c back wheel of the tandem bike. This issue was a planning error.