A turnbuckle is a device used to adjust the tension of cables, chains, or ropes. It consists of a central barrel with two threaded ends, each connected to a hook, eye, or other attachment point. By rotating the barrel, the threaded ends can be adjusted in or out, increasing or decreasing the tension in the cable or chain. Turnbuckles are commonly used in construction, marine, and transportation industries for tasks such as cable tensioning, leveling structures, and adjusting the length of straps or belts.