A turnbuckle, also known as a bottle screw or adjusting screw, is a device for adjusting the tension or length of ropes, cables, tie rods, and other tensioning systems. It consists of a pair of threaded rods, one with a left-hand thread and the other with a right-hand thread, and a body that connects the two rods. By turning the body, the tension in the ropes or rods can be adjusted. Turnbuckles are commonly used in rigging and construction, as well as in other applications where adjustable tension is needed.