Towing with a Truck – you need to read this especially.

The vast majority of caravan rigs on our roads are connected to the tow vehicle via a 50mm round tow ball and coupling.

How much do you really know about this vital but often disregarded piece of equipment?

I contacted several relevant state authorities to get the facts.



50 mm tow balls are only rated to 3,500 kgs. Larger 70mm balls or other hitch types are required above this weight. All hitch types are rated so ensure you have the right one for your towing job.

Transport for NSW advise that 50mm ball couplings must comply to ADR 62 and Australian Standard AS4177. A coupling complying with this standard must be permanently marked accordingly:

  • the manufacturer’s name or trademark;
  • the mark ‘50’;
  • the maximum rating for the coupling body in one of the following, as applicable,
  • 750 kg; or
  • 2000 kg; or
  • 3500 kg;
  • a code to indicate the serial number, batch, production date, or similar;
  • the words ‘DO NOT WELD’ if the coupling body is manufactured from nonweldable materials;
  • the words ‘WELD ONLY’ if the coupling body is specifically designed to be attached by welding only

This is quite a comprehensive list and similar in all states, and we have all seen many tow balls from overseas that do not comply with this standard. Does yours?

Note the different rating, are you using the correct rating and not just the one used to tow a box trailer that was on the vehicle.

The 50mm tow ball must also be fitted at a height of between 350 and 460mm of the ground to be compliant. This height limit is NOT noted relevant to other types of hitches. i.e., DO35, Hitch-Ezy etc.

This height limit will make safe coupling with many off road caravans and lifted tow vehicles difficult to comply with, but it is still the law and should be complied with.

Although they are by far the most used hitch, I am not a big fan of their use.

Yes, they are common and on most hire company trailers and useful for borrowing trailers. I have one on a special hitch for when I borrow my son-in-law’s box trailer.

The 50 mm coupling will have limited roll and once the limit is reached the caravan can in fact assist rolling over a tow vehicle in a caravan rollover situation. The cup rolls and pushes the stem to help tip the tow vehicle.

They are therefore not suited to, nor popular with serious off road towing.

Wear on the 50 mm ball can reduce its size and therefore, if not regularly checked and adjusted the coupling can become loose and jump off in some situations.

To grease or not to grease is a very contentious issue and open to debate. I grease mine as I believe all metal-to-metal friction areas should be lubricated to reduce wear.

I cover the greased tow ball with a cap when not in use to reduce dust etc. and mostly remove the hitch completely.

Many believe that greasing the ball attracts dust increasing wear. A fair point, however, this can be combatted by covering and regular maintenance practices, but it is personal choice.

Many 50 mm balls have not been changed, serviced nor coupling adjusted for many years and one wonders as to the reliability and size of the now worn ball and coupling.

Be very careful of fitting, or still having fitted an old imperial size ball. They are slightly different to the 50mm ball in sizing which may cause the coupling to jump off.

Adjust the ball regularly and it may also need adjusting when changing trailers and trailer couplings as size adjustments will vary.


Transport and Main Roads Qld advise the following;-

“There is no legal requirement to have a trailer hitch on a light vehicle certified by a qualified person. The replacement hitch will need to comply with AS 4177.1, section 6 requirements to have the mandatory markings. The markings can be placed on a permanently attached identification plate or directly onto the towbar. Towbar manufacturers can refer to AS4177.1 for details.“ 

Transport for NSW advise:-

A like-for-like or replacement component does not need to be assessed. It is recommended that a tradesperson with the appropriate qualification carries out the repair.

If the coupling is being replaced in order to achieve a higher ATM certification from the manufacturer or a recognised vehicle certifier would be required to re-rate the vehicles capacity. More information on light vehicle modifications can be found in the following link.

VSI No.6 Light vehicle modifications Rev 3 November 2013 ( “


If your tow vehicle has a GVM of 5,000 kg or above, a derating factor applies to the 50mm tow ball.

Even though the ball may be originally rated at 3,500 kgs, when you attach it to a vehicle with a GVM of above 5,000kgs you will not be able to tow a 3,500 kg van with this set up.

A notice may also need to be fitted to the tow vehicle stating the maximum trailer weight that can be towed with the 50mm ball.

For example, a tow vehicle with a GVM of 6,000kgs can only tow a trailer / caravan to a max of 3,089 kgs when using a 50mm tow ball. The trailer weight reduces dramatically the heavier the tow vehicle GVM gets. (7,500 GVM tow vehicle – 2,801 kg van etc.)

A full explanation, calculations and chart is available from the National Heavy Vehicle Regulator (NHVR).

Vehicle Standards Guide VSG16 – 50mm Ball Couplings (


Personally, I have a 200 series Landcruiser with GVM, GCM Lovells upgrade and increased towing capacity to 4t. I don’t usually tow that heavy as my van is only 3,300 ATM but it leaves me a safety margin.

I use a 5-tonne rated Hitch Ezy tow hitch which has automatic double locking. It is the best and easiest to fit that I have found. It is a very solid post with articulated coupling for off road and rollover. There are 3,500 kg rated ones available. They are also not as common, so they are harder to steal but fully lockable.

Hitch-Ezy | Tow Couplings | Caravan 4WD Towing

I get no commission unfortunately.

I trust that this has helped explain some of the complexities and laws around the simple 50 mm to ball.

Stay safe, and please check out our web site for more articles and information on safe caravanning.


Ken Wilson


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