Difference between 2" and 50mm Towballs - wobblyboot
A comment by SL on the motorhome towing thread reminded me of something that has puzzled me for a while.
Is the only difference between a 2" ball and a 50mm one 0.8mm? And if so, why is this enough for the two to be incompatible? I don't doubt that they are, I've been told in no uncertain terms never to mix them up, but surely the latch on the trailer hitch would accomodate some play, to allow for wear in the ball etc.
Or are they different shapes or something?
Difference between 2" and 50mm Towballs - Screwloose

As far as I can remember; it's not the size that's different, it's the way the trailer locks on to the ball.

The 50mm has an under-cut lip at the base of the ball [which must weaken it no end] for the hitch securing lug to lock into - a 2 inch ball doesn't, so the hitch handle can't lock down fully and can then jump off.
Difference between 2" and 50mm Towballs - Cliff Pope
I've just looked at my 50 mm ball and there is no such cutaway.

I remember years ago when both were commonplace the advice was that fitting the smaller hook over the larger ball was acceptable as long as it was not too tight (there was a tolerance anyway) but that hooking larger over smaller was not because of the possibility that it could jump off. Dinghy sailors I knew just tried it, and if it didn't seem too lose, they used it.

Remember there is supposed to be a connecting wire or chain just in case it does detach.
Difference between 2" and 50mm Towballs - bathtub tom
>>Remember there is supposed to be a connecting wire or chain just in case it does detach.

Isn't this just for braked trailers? I think you'll find it's designed to pull the brakes on, and then snap if the trailer should become detatched for any reason.

Many years ago, I bought a caravan that didn't have one fitted, although the hole was in the bottom of the brake lever. I fitted a chain.

The next time I used the 'van, I parked it up, disconnected the hitch, and drove away!
It took me a couple of hours of heaving to release the brake where it had pulled it on so hard!
Difference between 2" and 50mm Towballs - billy25
Even 750kg un-braked trailers need a safety chain, (our boat club insists on them being fitted) so that you can keep them to under a certain amount of control with your vehicle if they do detach, and so they don't go carreening off into oncoming vehicles.

Difference between 2" and 50mm Towballs - Screwloose

Your ball should have the ledge at the base of the ball. A 2" ball flares seamlessly from neck to sphere; a 50mm has a very defined step at the join.
Difference between 2" and 50mm Towballs - oldnotbold
"Isn't this just for braked trailers? I think you'll find it's designed to pull the brakes on, and then snap if the trailer should become detatched for any reason."

My 500kg Ifor Williams trailer came with a safety loop, despite having no brakes. Seems a good idea, and cost pennies. It's just 18" of wire rope.
Difference between 2" and 50mm Towballs - NARU
There is a big differenc between the two.

If the trailer has brakes, the safety cable is designed to pull on the brakes, and then fracture (ie. the trailer parts company from the car).

If the trailer does not have brakes, the safety cable/chain is designed to keep the car and the trailer together - ie not to fracture.
Difference between 2" and 50mm Towballs - 659FBE
Absolutely right. My Trelgo unbraked trailer has a loop of chain which would be strong enough to keep it attached to the towing vehicle. My twin axle braked horse trailer has a steel cable which operates the brakes if the coupling fails. I've no doubt it would then snap.

50 mm is a European standard - I've not seen a 2" balll for years. The 50 mm ball is readily identified by its having a flat ground on the top.

Difference between 2" and 50mm Towballs - Cliff Pope
I agree about the difference between chains and cables. I always understood it was a legal requirement to have a chain on an unbraked trailer, but may be it is just advisable. I have also been told that it is important that the chain or cable shackles to a special hook that is separate from the tow hitch assembly, otherwise both are vulnerable if the hitch collapses.

I have looked at a variety of my tow balls (I have 4 vehicles with balls, and several spares knocking around). All are 50 mm, but there is no consistency in design. Most are round, but one has a flat top. Most have no ridge, but two do (not the flat-topped one).

I do recall once having seen one that had a cut-awayvertical slot in the back. I have no idea what that was for - 2" pattern perhaps, or improved lubrication?
Difference between 2" and 50mm Towballs - zg

In case of any confusion a USA 2" ball, should not and will not, fit on to to a trailer with a 50mm socket

I imported a 2"Curt 45592 "Euro ball mount" from the USA, and it is simply too large for the ball to go into the socket. I have access to two trailers, one new one must be 50mm (made in Wales) and the other is cast and stamped 50mm. It will fit in neither. It is not a case of it not locking, but the ball not pushing in.

In theory it is 0.8mm larger but that seems to be enough. The 2" has a flat piece on top like EU models.

My USA manufactured tow hitch (they do not make it any more in the EU for my vehicle), has a square hole for the attachment which is 1 & 1/4 inch square (some are 2" square) I needed to purchase a 1 1/4 inch square end for a ball mount (not a Euro mount ball mount) and then purchase a 50mm ball in the EU which mounts in the 3/4 inch (19mm) hole. Most free fit balls that are available have 22mm M22 thread, so they will not fit.

Beware balls with a 19mm thread are often light weight designed for quad bikes etc. so make sure to get one rated for vehicle towing.

See here for the options:


Do NOT buy the Euro type as they will not work with 50mm

So to summarise, if importing a tow hitch from the USA to EU, you need to NOT buy a ball from a USA source, instead buy "ball mount" and get a ball in the EU that is true 50mm and designed to mount in the correct size round hole and fit it to it.

Ideally you should only souce tow bars in the EU, as they should comply with relevant EU leglisation and not have imperial and non typical ball sizes.

Others discussed this in Australia:


General info on tow hitch sizes here:


I will try take a photo and link to it at some stage.

Other things to consider is the ball height, and the trailer should be level and have the correct 'nose weight' so you need the correct rise or fall adapter, so the trailer should be consulated for the correct height and matched to the vehicle.

Difference between 2" and 50mm Towballs - zg

I have made some photos of my set up. I have a US style tow ball mount, but I am using a European suppled 50mm towball. This fits perfectly on to my 50mm coupling, but it is limited to US Class I rating and the ball is limited to 350KG mainly due to the 3/4" hole the ball is mounted on. I could not use a 2" ball as it simply would not fit either of the two 50mm couplings I tested.

Here is the photos promised with descriptions, showing why they are not compatible:



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