"Designed specifically for self recovery, hub capstans bolt directly onto the wheel rims and with a cable attached, the capstan winds up the line and hauls the vehicle out as the wheels spin. To overcome the effect of the axle differential, two capstans must be used simultaneously. Hub capstans can pull a vehicle free in both directions, are lightweight, easy to operate, very effective and are inexpensive. Because only a portion of the wheel nuts secure the capstan, it is not necessary to jack up the vehicle to remove them and therefore a single set can be used by a number of common vehicles."
dont know much about it just remember them on landrover 101 forward controls when i was a kid growing up in kenya where where is really bad black cotton mud.