I found this on the web but I have no first hand knowledge. I tried to find the TM but could not find the -1 if anyone has access?
The brackets, mounted to the wheels, are for self-recovery when a winch is
unavailable. A rod or bar is placed through each side and a cable or rope
attached. As the wheels spin, the rope winds around the bar/wheel assembly
and pulls the vehicle backward.The bolt holes are present on the front wheels because there is only one
type of wheel in use. The rear is only used because it will pull evenly and
it's typically easier to back out of a muck hole than forward deeper...
(Reference for concept, beyond training: FM 17-98-1, Scout Leaders Handbook,
Chapter 10, Section III and illustration 10-19)