Trailer Safety Chains and Shackles

Often when seeking information regarding meeting legal criteria such as for towing it can be difficult to find or interpret the correct answer. This is the case for many of the aspects of remaining legal whilst towing and we have made significant efforts to ask as many people as possible to find out what needs to be done to stay legal and we are going to present this in a series to you.

The first subject we’re going to discuss is trailer safety chains and shackles. What do you actually need to do to remain legal and most importantly safe?

Purpose of a safety chain

A safety chain is required on your trailer to provide an insurance if your hitch fails and breaks away from your tow vehicle. The safety chains are designed to reduce this risk of your trailer breaking free from your tow vehicle allowing you time to come to a stop and therefore reducing the risk of the trailer causing an accident or being damaged.

Safety chain rating

As you can imagine in the case of a hitch failing, the safety chains will have to deal with some significant forces and therefore are required to meet certain legal compliances as detailed in the relevant Australian Standards (referenced below). Of course unless you are building your own trailer, safety chain compliance should be handled by the manufacturer.

The below summarises safety chain requirements:

  • Trailers that do not exceed 2.5 tonnes ATM must have at least one safety chain complying with Australian Standard AS 4177.4-1994 or Australian Standard AS 4177.4-2004 ‘Caravan and light trailer towing components —Part 4: Safety chains up to 3500kg capacity’, or be a safety cable with a certified load capacity of the same;
  • Trailers over 2.5 tonnes and not exceed 3.5 tonnes ATM must have two safety chains of designation of 3500 kg complying with Australian Standard AS 4177.4-1994 or Australian Standard AS 4177.4–2004;
  • Trailers over 3.5 tonnes ATM must have two safety chains made from steel of a minimum 800 MPa breaking stress that conforms to the mechanical properties of Grade T chain as specified in Australian Standard AS 2321-1979 ‘Short Link Chain for Lifting Purposes (non calibrated)’ or Australian Standard AS 2321-2006 ‘Short Link Chain for Lifting Purposes.’ Each chain must be sized such that the minimum breaking load exceeds the ATM.



Shackles are an interesting topic to get to the bottom of as it takes some interpretation of the ratings.

It turns out when choosing a correctly rated shackle the designation on the shackle is not entirely relevant to the application of securing a trailer safety chain. The common rating printed on a rated shackle is WLL or Working Load Limit. This limit is relevant to lifting applications and not for the forces relevant in a trailer safety chain application, where the relevant rating is actually what is called the minimum breaking strength.

To help interpret this please refer to the following extract from the Department of Infrastructure and Regional Development; CIRCULAR 0-1-3 – SAFETY CHAIN CONNECTION DEVICES FOR ROAD TRAILERS WHICH ARE UP TO 3.5 tonnes (3,500kg) AGGREGATE TRAILER MASS (ATM):

Shackles used to attach safety chains to towbar attachment points should at a minimum exceed the required rating of the safety chain, as determined by the ATM of the road trailer. Additionally, the shackle should be fit for purpose and compatible with the safety chain in terms of strength and size. This may be fulfilled by:

  1. The use of a shackle that is compatible with the safety chain and complying with AS 2741. In this case, the shackle must have appropriate markings, as identified below:
    • Manufacturers Identification;
    • Quality or Grade as M or 4, or S or 6;
    • WLL, the maximum load that may be applied to the shackle; and
    • Identification marking to trace the shackle to a test certificate.
Trailer ATM (kg) For Bow or D-Shackles complying with AS 2741      
  Minimum shackle Working Load Limit (WLL) (kg) Minimum size of shackles (Body diameter, not pin size)    
    Grade M (or 4) D-Shackle (mm) Grade S (or 6) D-Shackle (mm) Grade S (or 6) Bow-Shackle (mm)
0-1,000 250 6 6 5
1,001-1,600 400 10 6 6
1,601-2,500 625 13 8 8
2,501-3,500 875 16 10 10

Table 1 – Typical shackles recommended based on trailer ATM

2. Alternatively, the use of a shackle that is compatible with the safety chain and is of a reputable brand. In this case, the shackle will have appropriate markings to show the brand and or part identification sufficient to trace its brand and strength back the original manufacturer.

Source: Department of Infrastructure and Regional Development

Crossing the chain

Another topic for discussion is that about crossing the chains when attaching a trailer with 2 chains to your vehicle.

In our research we were unable to  find legal reference to the requirement to cross the chains however we would recommend this practice based on the sound logic behind it.

By crossing your chains, that is attaching the right trailer chain to the left vehicle attachment and vice versa, you effectively create a chain cradle that will help to hold your hitch off the ground in the event of a breakaway.


Such a simple topic in theory, and so many trailers out there being used every day, but as with all legislation it can be difficult to properly understand what needs to be done to remain compliant and above all remain safe!

Of course if you are interested in hiring a camper trailer or caravan we at Make Trax Adventure Hire ensure that our rigs are legal and you remain informed on what you need to know. If you’re interested in hiring an awesome rig check out our fleet at

Let us know if you have anything to add to this topic!

Useful References