A turnbuckle is a mechanical device used to adjust the tension or length of cables, ropes, or rods. It typically consists of two threaded eye bolts (or hooks) on each end, connected by a metal frame or body that has a central turnable section. This central section can be rotated to either tighten or loosen the connection between the eye bolts, thus adjusting the tension of the assembly.

The primary purpose of a turnbuckle is to provide a simple means of adjusting the tension in various applications, such as in sailing rigging, construction, tensioning fences or cables, and supporting structures like bridges or radio towers. By turning the central section clockwise or counterclockwise, you can either increase or decrease the distance between the two ends, thereby controlling the tension of the cable or rod.

Turnbuckles are available in different sizes and materials, including steel, stainless steel, and other alloys, depending on the specific application requirements. They come in various configurations to suit different load capacities and environmental conditions.