A snatch block is a sheave, or pulley, that would be chained or strapped to a tree or another vehicle. You run your winch line through the sheave and back to your vehicle. It will double your pull but it will decrease the speed by half. But if your in such a bad situation you need a block you wont care about how fast your winch pulls, but be aware your line will only be half as long since it's running to the sheave then turning back around and hooking to your truck.
