Turnbuckles

A turnbuckle is a rigging device used to provide even tension on flexible rigging elements. Its design is based on a cylindrical body with oppositely directed threads on its parts: tightening or loosening the screws adjusts the tension of the rope.

Applications:

• Installation of structures and bridge stay cables;
• Lifting loads;
• Shipbuilding and yachting;
• Antenna fastening;
• Tent installation;
• Installation of auxiliary support devices.

Turnbuckle design

Turnbuckles differ in appearance and operating conditions.

Body variants:

• By coupling type — open and closed turnbuckles;
• By manufacturing method — welded and stamped products. This category includes the open-coupling turnbuckle that complies with DIN 1480.

A separate category is the chain turnbuckle, also known as a ratchet.

By fastening configuration, the following types are distinguished:

• Hook-hook;
• Eye-eye;
• Fork-fork;
• Eye-fork;
• Hook-eye;
• Hook-fork.

The turnbuckle design is simple: an elongated cylinder or an elongated ring, hollow inside. At the ends of the product there are threaded holes sized for a specific screw, which are tightened toward each other. A bolt with matching thread is inserted into the hole, with an additional fitting on its head for securing flexible rigging elements.

The body can be of closed or open form. The closed form is used outdoors, since moisture that could jam the thread cannot get into the screw mechanism.

Material

Turnbuckles are made of high-strength steel grades per GOST 1050. The strength level can reach 540 MPa. After initial heat treatment, the tensile strength is not less than 450 MPa. Such turnbuckles are intended for use under standard conditions.

For use in aggressive environments, turnbuckles are additionally coated with protective layers:

• Electroplating;
• Hot-dip galvanizing;
• Lamellar coating.

Fasteners for very aggressive environments are made of austenitic stainless steel, which offers increased durability when used in environments with reduced pH.

Marking

Turnbuckle marking contains the full list of parameters: head, coupling length and other elements excluding ring dimensions, indicating the side on which a particular thread is located. The marking is duplicated in the accompanying documentation.

Load capacity depends on the product type, the type of fitting on the screw and its diameter, and is specified in the accompanying documentation. This must be taken into account when selecting a turnbuckle.

Characteristics are specified in the GOST, DIN or batch documentation. For example, for M6 marking, the load capacity is 40 kg for a hook and 100 kg for an eye.

Marine turnbuckles are the most expensive.

The most common sizes:

• M6;
• M8;
• M10;
• M12.

How to choose?

Turnbuckle selection is based on the load’s operating parameters and conditions of use. For securing suspended loads, products with a greater margin in weight and load capacity should be used in case of unforeseen circumstances.

An important factor is employee safety, which depends on the degree of rope engagement in work processes. Products with a fork-fork fastening system, where the hook is secured with a special high-strength pin, are considered the least hazardous.

Load capacity, t	a, mm	b, mm	c, mm	d, mm	Weight, kg/pc
13	24	400	16	210	3
20	30	400	20	210	5