A turnbuckle, stretching screw, or bottles crew is a device for adjusting the tension or length of ropes, cables, tie rods, and other tensioning systems. It normally consists of two threaded eye bolts, one screwed into each end of a small metal frame, one with a left-hand thread and the other with a right-hand thread. The tension can be adjusted by rotating the frame, which causes both eye bolts to be screwed in or out simultaneously, without twisting the eye-bolts or attached cables.
Three major types of end fittings can be used together in any combination on either end of the turnbuckle:
Hook end: a hook end fitting is used to create temporary connections because these are easy to connect and disconnect. These should not be used in connection where the tension could release unexpectedly.
Jaw end: a jaw end fitting comprises jaw and bolts secured together by a pin or nut. These are used to connect to components that cannot be opened.
Eye end: An eye fitting is a closed loop that can be connected to a shackle or quick link.
Turnbuckles can be used for something as simple as a fence or as complicated as a suspension bridge. Turnbuckles are commonly used in:
Sports and entertainments
Maritime transport
Construction
Aviation
DIN, IS, ISO, EN, ASME, and all international standards
The most common turnbuckle material is stainless steel. Stainless steel turnbuckle is ideal for use in saltwater environments and outdoor. Especially if corrosion is a concern stainless steel turnbuckles are the best choice. Other than that, other materials are used for construction
Thread diameter: the diameter is the measurement of the threaded part of the end fitting. The greater the thread diameter is greater the load-bearing capacity of the turnbuckle and vice versa.
Take up length: it is the total length that the ned fitting can screw into and out of the body to hold tension. Take-up length can be measured in terms of opened or closed-end fittings: the end fittings are either fully extended or fully retracted.
Galvanised
Zinc plated
Black oxide coated
Phosphate coated