Bit of debate with what you can/can't use instead if a shear pin, some people use bolt, but others will post what they use.
The pin is usaully just behind the winch itself, the shaft comes out of the winch, to the main driveshaft, where the pin goes.
Some people run one at the other end of the shaft, just off the gearbox, if this is the case, put a bolt in here, and run a shear pin at the front, that way the weakest point is at the front where its easy to get to.
Hope that makes sense
Dave