Threefold purchase

On a ship, blocks, otherwise known as pulley wheels, are used to operate lifting elements that require a lot of force or a change in direction of thrust. Together with the rope, they form a block and tackle, or just a tackle in sailing. These are found at the rigging and spars. They can also be used to trim or ease sails, but also to carry heavy objects. Blocks can be single, double, or threefold, in which case they allow one, two, or three ropes to be threaded through them independently. They come with one or two hooks, rounded loop or square bracket versions. The featured threefold purchase is fitted with up to three steel lugs, consisting of flat bars set between the cheeks and inserts. Leszek Kocela