A Snatch Block is a pulley system

A Snatch Block is a pulley system to aid with power winches. Using a snatch block can effectively allow you to double the line which in turn doubles the lifting capacity of the snatch block and winch arrangement. A single snatch block or multiple snatch blocks can be deployed in conjunction with a winch to maximise lifting load capacity. Snatch blocks are commonly used in the lifting and marine industry, since they are a simple mechanism to extend the lifting capacity of winches.