A turnbuckle is a way to add tension. Made up of two fittings and a central, adjustable length body, a turnbuckle is activated by turning the body, which adjusts the distance between the two fittings. It is this simplicity of design that has spanned the decades of use in rigging, construction and engineering.
When the need to put a wire rope, chain or other material under tension is present, you will find a turnbuckle. Turnbuckles can be found on masts, attached to scaffolding, and securing a load to a truck. The goal is to eliminate slack and maintain tension, all while keeping the connection loose.
What is a Turnbuckle and What are It’s Purposes?
The choice of end type determines the type of assembly connection a turnbuckle can make. Hook end turnbuckles are easily assembled and disassembled, however, their connection is easily defeated by either lifting or slack, therefore, they are unsuited for any application where connection could be lost. In applications such as lifting or rigging work, eye ends are preferred and are further secured by the use of a shackle. Jaw ends provide a positive connection to a pin or bracket, thereby preventing any movement of the connection. A combination of jaw and eye ends of a turnbuckle is typical and is useful for most applications of structural rigging.
As for the materials used in construction of turnbuckles, stainless steel is preferable in marine and coastal environments to resist corrosion, whereas in constructing lifting equipment, carbon steel, which is galvanized or zinc plated, is adequate. However, the quality of the steel is very important. In lifting applications, turnbuckles must be rated and marked to indicate their Working Limit Load. General merchandise turnbuckles must never be used in lifting applications as they are of a lower quality.
Gradually increase tension evenly on the body. Rapidly tightening the body creates a concentrated force on the threads and can result in galling. Galling makes removal and adjustment of the turnbuckle almost impossible. When the proper tension is created, the turnbuckle must be locked off. The body can gradually rotate, relax the tension, and even slip back. This can happen under a vibrating load or under a repeated loading/unloading cycle. A locking nut at each end with a fitting or a safety wire through the body will prevent this from happening. Corrosion on the threads can occur over time if the turnbuckle is left outdoors. Unusable turnbuckles must be removed from the lifting assembly.
When a turnbuckle is a part of a lifting assembly, such as in a spreader beam, it is a lifting accessory under LOLER. It must be rigorously inspected every six months by a competent person, and it must be marked with its WLL. If a turnbuckle lacks a WLL tag, it must not be used in a lifting application.