A turnbuckle is also called a bottle screw or a stretching crew because it has the “stretching” effect on ropes, cables, and other tensioning systems when the tension or length is adjusted.  A turnbuckle can consist of two threaded bolts: an eye bolt and a hook bolt screwed into each end of a small metal frame. Sometimes, it can be two eye bolts.

A turnbuckle has many uses, usually one that needs a lot of tension. Because of this, a turnbuckle can vary in size and weight–from the ten-gram turnbuckle for a home application to a thousand-kilogram one for bridges and buildings. Turnbuckles are secured with either a wire clip or a lockwire 

In aircraft, a turnbuckle is used to adjust the tension on structural wires for the wings and on flexible cables for the flight control systems. In shipping, a turnbuckle is used for rigging and lashing. In sports, a turnbuckle is used for boxing rings or wrestling rings to adjust the tension of the ropes.