Trailer couplings, chains and D-shackles
  |  First Published: June 2015

When it comes to towing your trailer, there are a few things to keep in mind regarding the coupling, safety chain and D-shackle. If you’re not aware, all parts related to towing need to be correctly marked and rated with the Australian Standard. If they are not, then you may be towing illegally.


There are 2 sizes a trailer coupling can be in Australia — 50mm or 70mm. The most common is 50mm. These couplings are on all trailers that have an Aggregate Trailer Mass (ATM) of between 750kg and 3500kg. It does not matter if the trailer has brakes or not, as it’s irrelevant when it comes to the size of the coupling.

If your coupling is not marked with an ‘AS’ (Australian Standard) number or have 50mm or 70mm stamped into it, then make sure you get it checked out. Other reasons to be concerned with your coupling include:

Coupling component is loose or cracked.

Coupling does not display Gross Mass Rating.

Any mounting bolts, fasteners or weld beads have advanced corrosion.

It is now common to see markings on chains and D-shackles, but if yours are not marked, don’t worry. You can contact the trailer manufacturer and have them send you certification on the chains fitted.

Other chain issues that are deemed a defect include:

If the chain is not permanently attached to the draw bar.

If the chain touches the ground.

If the chain links are bent, broken or ground down in size.

If you have any questions relating to your trailer’s coupling, chain or D-shackle, make sure you seek professional advice from an Authorised Trailer Inspection Station, or feel free to contact Bold Trailers for all your trailer needs.


Chain and D-shackle standards can get confusing, especially if you don’t know what size is the minimum for your trailer. Here is a guide:


Up to 1000KG6.3mm9.5mm
Over 1000KG up to 1600KG8.0mm12.7mm
Over 1600KG up to 2500KG10mm12.7mm
Over 2500KG up to 4500KG7.1mm x 2 Chains12.7mm x 2 D-shackles
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