Turnbuckles and rigging screws

Working with wire rope slings and chain? Use this page to find out how to safely use turnbuckles and rigging screws.

What are turnbuckles or rigging screws?

Turnbuckle or rigging screws are used for:

• tensioning, or
• fine length adjustment of wire rope slings and chain.

They are also called bottle, union or stretching screws. They should comply with AS2319 Rigging screws and turnbuckles.

Turnbuckles or bottle screws all have a left hand thread at one end and a right hand thread at the other.

The nominal size of a turnbuckle is taken from the thread diameter.

Turnbuckle

Using turnbuckles or rigging screws safely

They can be shortened or lengthened by twisting the frame or bottle. They can be very dangerous where vibration causes them to unscrew.

Industry recognised methods of securing turnbackles or bottle screws to prevent unscrewing under vibration include:

• locknuts, or
• moussing (for example, conveyors).

With lock nuts

Before use, the thread inside the bottle or frame must be examined for:

• slackness
• wear
• over extension.

The screw thread is easy to see and examine for defects.

Standard requirements

Australia Standard 2319 covers grade 'L', 'P' and 'S' turnbuckles and rigging screws used for restraining or lifting.

The standard requires each item to have:

• a proof load of twice the working load limit
• a minimum breaking strain of six times the working load limit
• in addition, 15% elongation.

The standard covers sizes from 10mm to 100mm (inclusive).

Acceptable end fittings are:

• round eyes
• elongated eyes
• drilled eyes
• clevis end.

Bodies can either be:

• open as for turnbuckles, or
• closed as for rigging screws.

Turnbuckles and rigging screws are marked with:

• grade 'L', 'P' or 'S'
• working load limit (WLL)
• manufacturer's identification
• nominal size
• correlating mark to proof load test certificate.

In this standard, two body lengths are given: standard and short. The length of the body depends on size.

Thread inspection holes in rigging screws must always be kept clear