A block is a set of pulleys or sheaves mounted on a single frame. An assembly of blocks with a rope threaded through the pulleys is called tackle. A block and tackle system amplifies the tension force in the rope to lift heavy loads. They are common on boats and sailing ships, where tasks are often performed manually.

In the diagram shown here, the number of rope sections of the tackles shown is as follows:

• Gun tackle: 2
• Luff tackle: 3
• Double tackle: 4
• Gyn tackle: 5
• Threefold purchase: 6

Note that the gun tackle, double tackle and threefold purchase all have the same number of pulleys in both blocks (one, two and three, respectively) whereas the Luff tackle and Gyn tackle have mis-matched blocks with differing numbers of pulleys.