Chains & Shackles

Chains and shackles are important components in the safety of your trailer and should not be overlooked or given the attitude that any chain and shackle will do.

There are so many trailers in this country running with an old bit of chain left over from some long forgotten job and an even smaller D shackle that lost its original pin many years ago and is held in place with a bolt or screw that only just fits.

If in the unfortunate circumstances that your trailer decides to leave the comfort of your vehicles tow bar at 90km/hr, you have a trailer barreling full blast down the road un-guided and unhindered into any poor soul that may be on the road at the same time.

Poorly chained and shackled trailers do come loose and do kill and maim people.Chain_and_shackle.png

One issue that does crop up on a regular basis is that tow bar manufacturers drill too small a hole to incorporate a rated shackle, hence the rated shackle is thrown away and anything that fits is used.

At the time of writing this, it was not illegal to drill the shackle hole out to fit the rated shackles as long as there was plenty of material around the new hole.Quicklok_chain.png

If you are not keen to drill your existing towbar shackle hole bigger or can’t be bothered with using shackles full stop, you can purchase and bolt on a “Quick Chain Connector”. These use a spring loaded pin to retain and release the chain without use of a shackle. Just make sure that both the “quick chain connector” is rated to your requirements and that it fits your rated chain(s).

On trailers up to 2000kg GVM (Gross Vehicle Mass -  trailer tare weight and load combined) only one chain is legally required. According to the NZ Code of Practice, the chain needs have a breaking strength of at least 4000kg. The rating on the chain and shackle is normally the safe working load rating and has a much higher breaking strength. If unsure, check with your supplier on this before purchasing .

On trailers with a GVM between 2000kg and 2500kg, double crossed chains are required.

Trailers over 2500kg to 3500kg are required by law to have a "break away" braking system in place and safety chains are not required. Personally, I like to have at least one chain fitted as well for peace of mind.

NZ Code of Practice NZS5467:1993

The code of practice for chains and shackles in New Zealand are as follows –

1. Safety connection(s) shall have a minimum breaking strength equal to 2 times the maximum towed mass.

(If you are towing a trailer with a combined tare weight and load of 2000kg, you are required to have chains with a combined minimum breaking strain of 4000kg)

2. The safety connection(s) attachments shall have a strength equal to, or greater than the safety connection.

(Any bolts or other forms of connection of the chain and shackle to the trailer or tow vehicle, need to be rated as strong or stronger than the safety chain and shackles)

3. The attachment of the safety connection(s) to both the towbar and drawbar shall be separate from the coupling and its fastenings.

(Do not use the coupling bolts to bolt your safety chain to the trailer)

4. The safety connection(s) shall be mechanically fitted as close as is practicable to the longitudinal centre line and of such length that in the event of coupling failure, it will prevent the drawbar hitting the ground as well as controlling the direction of the trailer to follow the towing vehicle.

(Attach the chain as close as practical to the coupling and keep the chain as short as practical without interfering with full lock steering)

5. Welding of the chain is not acceptable.

(Use a high tensile bolt and safety chain mounting washer to attach your chain to the drawbar – also keep any holes drilled in the drawbar at least ½ to ¾ the length of a chain link from the outside edge)

6. The safety connection(s) shall be indelibly marked by the component manufacturer with their rating. The rating shall enable the minimum breaking strain of the components to be identified.

(Both chains and shackles need to have the manufacturers rating either stamped or cast into their surface. Note that some chains have the rating stamped every couple of links)

Australian Safety Chain & Shackle Regulations

All safety chains on trailers up to 3500kg ATM, must be permanently attached to the trailer by either bolting or welding, the use of shackles to attach the chain to the drawbar is not permitted.

If the chain is to be welded, the weld must extend around 50% of the link and the adjoining link must have free movement.

For trailers over 3500kg ATM, the safety chain/drawbar attachment must not be welded or have the chain deformed in any way.

The safety chain attachment must be located as near as practicable to the coupling and where there are 2 attachment points, they are required to be mounted on either side of the centreline of the drawbar.

Australian Standard AS 2741-2002 for Shackles

For trailers up to 3500kg ATM shackles are required to be
1. The shackle is required to be rated and comply with the Australian Standard AS 2741-2002 “Shackles” or other equivalent recognised standard

2. The break load limit of the shackle is rated at least 1.5 times greater than the ATM of the trailer.
(If you trailer has an ATM of 1000kg, the break load limit needs to be at least 1500kg)

3. Shackles need to be legibly and permanently marked with the following information.

A. The manufacturer's name or trademark;

B. Quality grade of the shackle, e.g. (“M” or “4”, “S” or “6”);

(Grade “M” or “4” shackles are around 20% stronger than their mild steel counterparts and are normally recognised by the pin having a larger diameter than the shackle material. “M” shackles are not so common now as they have been superseded by the stronger “S” shackle. Grade “S” or “6” shackles again have a larger diameter pin which is normally painted to differentiate from lower strength shackles. Grade “S” or “6” are higher in strength than the “M” or “4” grade although have less ductility. They tend to be smaller than the “M” or “4:” shackles for their respective ratings.

C. Working Load Limit (WLL) or Rating; and

D. Identification marking in order to correlate shackle to test certificate.

Nominal Shackle
Size (mm)
Working Load
Breaking Load
Grade Marking
5 330 1987 S or 6
6 250 1508 M or 4
6 500 3007 S or 6
8 750 4505 S or 6
10 500 3007 M or 4
10 1000 6004 S or 6
11 1500 9001 S or 6
13 750 4505 M or 4
13 2000 12040 S or 6
16 1500 9010 M or 4
16 3200 19285 S or 6
19 2000 12040 M or 4
19 4700 28265 S or 6