A turnbuckle is a device for adjusting the tension or length of ropes, cables and tie rods.
We uses turnbuckles extensively in Shade Sail installation.
A turnbuckle normally consists of two threaded eyelets, one screwed into each end of a small metal loop, one with a left-hand thread and the other with a right-hand thread. The tension can be adjusted by rotating the loop, which causes both eyelets to be screwed in or out simultaneously.
Turnbuckles are used in any application that requires a great deal of tension. They can range in mass from about ten grams for thin cable used in a garden fence, to thousands of kilograms for structural elements in buildings and suspension bridges.