A turnbuckle is a evice for adjusting the tension or length of ropes, cables and tie rods. It 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 most commonly used in applications which require 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. This device is also known as a bottlescrew and is used on ships for tensioning rigging and lashings.