Pulleys and snatch blocks or pulley blocks are used in all aspects of the lifting gear, hoist equipment supply, rigging and winching industries they are a simple method of creating mechanical advantage or changing the direction of a force being exerted.
In winching or lifting configurations the pulley block or snatch block will provide significant mechanical advantage if rigged correctly. For example if an off-road vehicle like a LandRover defender equipped with a 2.5t winch is stuck. Its winch cable can be attached to a tree where upon engaging the winch there will be 2.5t of force in the cable between the stuck LandRover and the tree. If the Land rover is really stuck and this configuration of winch cable does not free it a snatch block or pulley block can be used to increase mechanical advantage. Simply pass a chain sling, nylon sling, polyester websling or wire rope sling around the tree and attach it to a single sheave snatch block or pulley block using a bow shackle or safety bow shackle.