New towbar - what size ball?

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    Posted: 13 Feb 2020 at 9:58am
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new car doesnt have a towbar on the back - so getting one installed next week - should i be asking for 1 7/8" or 50mm?

current boat trailer coupling is one of those dual-fit models that can fit either sized ball - but i would like a tow ball that can accommodate other trailers that i might be towing in the future - are 50mm couplings becoming more common now?

also - does anyone know if there is a significant difference in the strength ratings of the two sizes? obviously there is a minor difference in ball diametre but what about the threaded shaft it sits on?

car is rated to 2500kg - so will be asking supplier to install towbar to match.

regards lighting connection - i am tempted to ask installer to just run the flat-pin type plug into the boot area with a bit of slack - my thoughts are that the connection stays a lot cleaner in the boot, doesnt tend to get smashed off if the rear of the car gets grounded - i would have enough length so that when the boat is hooked up that the cable gets run out and the boot closed on it - your thoughts on this arrangement? 
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Post Options Post Options   Likes (0) Likes(0)   Quote Kevin.S Quote  Post ReplyReply Direct Link To This Post Posted: 13 Feb 2020 at 11:17am
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I'm pretty sure the differently rated tow balls have different sized mounting threads on the bottom of them.  I discovered this when I tried to fit the wrong ball onto my tow bar and it wouldn't fit the hole that was in the bracket.
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Post Options Post Options   Likes (0) Likes(0)   Quote MB Quote  Post ReplyReply Direct Link To This Post Posted: 13 Feb 2020 at 12:01pm
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Post Options Post Options   Likes (0) Likes(0)   Quote terrafish Quote  Post ReplyReply Direct Link To This Post Posted: 13 Feb 2020 at 12:11pm
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Originally posted by MightyBoosh MightyBoosh wrote:

https://www.supercheapauto.co.nz/p/trojan-trojan-tow-ball-duo-fit---3500kg-1-inch/339108.html

Yep got one on the back of my van. Very handy and easy. Just make sure you keep the spare ball safe. I keep mine wrapped in a rag with the jack
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Post Options Post Options   Likes (0) Likes(0)   Quote FizFisho Quote  Post ReplyReply Direct Link To This Post Posted: 13 Feb 2020 at 4:10pm
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Originally posted by terrafish terrafish wrote:

Originally posted by MightyBoosh MightyBoosh wrote:

https://www.supercheapauto.co.nz/p/trojan-trojan-tow-ball-duo-fit---3500kg-1-inch/339108.html

Yep got one on the back of my van. Very handy and easy. Just make sure you keep the spare ball safe. I keep mine wrapped in a rag with the jack


Yep very handy for only $90.

How is the height of the bar or you have a square hitch mount receiver BH?

I also find the Trojan square hitches to be good quality.

Also I think thats a good idea ie the Cable. I had excess on my last boats trailer (is how it came) and when it went over a speedbump shared straight through the excess cable running along the trailer bar., must have just been a bit jammed under the bar and the speedbump. Got home and a bunch of my fuses were blown.
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Post Options Post Options   Likes (0) Likes(0)   Quote Mr Moritz Quote  Post ReplyReply Direct Link To This Post Posted: 13 Feb 2020 at 5:33pm
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I need both sizes. If picking up a load of posts for fencing I use the free tandem there which is 1 7/8". If picking up a load of garden mix I use their free trailer 1 7/8". If using my own tandem I use 50 mm. If I am towing boat I can have the option of 1 7/8" or 50 mm. I colour code my tow balls to prevent mistakes. I use cordless torque wrench to put them on or off. Too easy.
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Post Options Post Options   Likes (0) Likes(0)   Quote Bounty Hunter Quote  Post ReplyReply Direct Link To This Post Posted: 13 Feb 2020 at 11:11pm
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Post Options Post Options   Likes (0) Likes(0)   Quote Dagwood Quote  Post ReplyReply Direct Link To This Post Posted: 14 Feb 2020 at 6:26am
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Drifting slightly, the introduction of the 50mm coupling appears be pointless. 

They don't carry a higher rating. All it has done is increase confusion and provide an opportunity for someone through ignorance or error to make a potentially fatal mistake.

Am I missing something?
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Post Options Post Options   Likes (0) Likes(0)   Quote Big -Dave Quote  Post ReplyReply Direct Link To This Post Posted: 14 Feb 2020 at 7:20am
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Yeah, you can out a 50mm coupling on a 1 7/8 ball, but it's loose..
Theoretically the safety chains should hold if something comes adrift, but who would want to bank in that.
Lots of euro stuff comes in 50mm. Caravans and trailers.
Dual sized balls are great, but I found the one with the pin through the ball, if you didn't change it regularly , the pipin seized, and you had to whack the snot out of it to get it off.
All of my trailers have been 1 7/8, so that's the ball I have.
you can't fix an idiot with duct tape, but it does muffle them for a while...
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Post Options Post Options   Likes (0) Likes(0)   Quote bazza Quote  Post ReplyReply Direct Link To This Post Posted: 14 Feb 2020 at 8:40am
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Owners of some models of European vehicles face an even greater dilemma inasmuch as the towbars they come factory fitted with have a mechanism whereby pressing an internal button turns the ball over
then retracts it.
 
Providing it does not malfunction is handy function perhaps for reducing the overall length of the vehicle when required but incorporates a 50 mm ball & is so designed that the ball cannot be easily converted without replacing the entire assembly which is very involved & ultra expensive. 
 
 
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Post Options Post Options   Likes (0) Likes(0)   Quote Mr Moritz Quote  Post ReplyReply Direct Link To This Post Posted: 14 Feb 2020 at 8:52am
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Originally posted by Dagwood Dagwood wrote:

Drifting slightly, the introduction of the 50mm coupling appears be pointless. 

They don't carry a higher rating. All it has done is increase confusion and provide an opportunity for someone through ignorance or error to make a potentially fatal mistake.

Am I missing something?


Couldn't agree more. It was done in the change over to metrics. As is typical in NZ we had to change everything. Britain kept gallons and mph. Very easy to put a 50 mm trailer onto a 1 7/8" tow ball there by creating an accident waiting to happen. 
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Post Options Post Options   Likes (0) Likes(0)   Quote bazza Quote  Post ReplyReply Direct Link To This Post Posted: 14 Feb 2020 at 11:15am
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Originally posted by Mr Moritz Mr Moritz wrote:

Originally posted by Dagwood Dagwood wrote:

Drifting slightly, the introduction of the 50mm coupling appears be pointless. 

They don't carry a higher rating. All it has done is increase confusion and provide an opportunity for someone through ignorance or error to make a potentially fatal mistake.

Am I missing something?


Couldn't agree more. It was done in the change over to metrics. As is typical in NZ we had to change everything. Britain kept gallons and mph. Very easy to put a 50 mm trailer onto a 1 7/8" tow ball there by creating an accident waiting to happen. 
If memory serves me well Maurice then the prevalence of the 50 mm ball far preceded decimal changeover & was then due to US equipment ( including ww11 war surplus ) that were fitted with what was then known as 2 inch.
 
As a youngster ( suffice to say more years ago than I care to remember ) can recall my dad had 2 size tow balls that he would change over accordingly. 
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Post Options Post Options   Likes (0) Likes(0)   Quote Mr Moritz Quote  Post ReplyReply Direct Link To This Post Posted: 14 Feb 2020 at 4:02pm
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First time I encountered 50 mm was after we changed to metrics. There were articles in newspapers about the change. They may have been here previously but I had only seen and used 1 7/8" till metrics.
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Post Options Post Options   Likes (0) Likes(0)   Quote bazza Quote  Post ReplyReply Direct Link To This Post Posted: 14 Feb 2020 at 4:44pm
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Originally posted by Mr Moritz Mr Moritz wrote:

First time I encountered 50 mm was after we changed to metrics. There were articles in newspapers about the change. They may have been here previously but I had only seen and used 1 7/8" till metrics.
 
In retrospect it begs the question of why settle on such an obscure dia as 1 7/8 " rather than a more logical 2 " ?
 
Guess there are many such examples in lots of the imperial system  suffice to mention but a few :-
 
303 calibre ammo when reducing by a mere three 1/1000 of an inch would have made it interchangeable with the US allies.
 
Weight :- 16 oz to a pound, 14 pounds to a stone (think that is correct) then to further confuse the issue it takes 112 pounds to make 1 x hundredweight ( go figure )
 
Currency :- 2 x halfpennies = a penny ... 3 x pennies a thruppence
2 x thruppence = sixpence, 2 x sixpence = a shilling, 10 x shilling = ten shillings ( who would have guessed that ?) 2 x 10 shillings = pound then to continue the illogic 2 x shillings = florin, 1 x florin plus sixpence = half crown, 2 x half crowns = a crown then a pound plus a shilling = a guinnea
 
Measurement :- 32 x 1/32 = one inch, 12 x inch = foot, 3 x feet = a yard then some obscure number of yards = a mile.
 
Volumes :- 20 fluid oz = pint, 2 x pints = quart, 4 x quarts = gallon
 
No I phones or even calculators back then ... we simply worked it all out mentally ... how many youths could do so these days ???
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Post Options Post Options   Likes (0) Likes(0)   Quote Mr Moritz Quote  Post ReplyReply Direct Link To This Post Posted: 14 Feb 2020 at 7:30pm
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Originally posted by bazza bazza wrote:

Originally posted by Mr Moritz Mr Moritz wrote:

First time I encountered 50 mm was after we changed to metrics. There were articles in newspapers about the change. They may have been here previously but I had only seen and used 1 7/8" till metrics.
 
In retrospect it begs the question of why settle on such an obscure dia as 1 7/8 " rather than a more logical 2 " ?

[ They probably designed the coupling at 2 inches and then wanted a ball to fit that and came up with 1 7/8"]
 
Guess there are many such examples in lots of the imperial system  suffice to mention but a few :-
 
303 calibre ammo when reducing by a mere three 1/1000 of an inch would have made it interchangeable with the US allies. 
 
Weight :- 16 oz to a pound, 14 pounds to a stone (think that is correct) then to further confuse the issue it takes 112 pounds to make 1 x hundredweight ( go figure )
 
Currency :- 2 x halfpennies = a penny ... 3 x pennies a thruppence
2 x thruppence = sixpence, 2 x sixpence = a shilling, 10 x shilling = ten shillings ( who would have guessed that ?) 2 x 10 shillings = pound then to continue the illogic 2 x shillings = florin, 1 x florin plus sixpence = half crown, 2 x half crowns = a crown then a pound plus a shilling = a guinnea
 
Measurement :- 32 x 1/32 = one inch, 12 x inch = foot, 3 x feet = a yard then some obscure number of yards = a mile.
 
Volumes :- 20 fluid oz = pint, 2 x pints = quart, 4 x quarts = gallon

[All that was drummed into me at a very young age, by teachers walking around with canes in their hands and eager to use them. Imagine if that happened to the kids of today]
 
No I phones or even calculators back then ... we simply worked it all out mentally ... how many youths could do so these days ???
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Post Options Post Options   Likes (0) Likes(0)   Quote Bounty Hunter Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar 2020 at 10:36am
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have kept things simple and fitted a 1 7/8 ball to new bar.

supplier recommended this as still by far the most common size. locally-built trailers are still being fitted with this size coupling, and any rental trailer that i might one day encounter most likely to be this size also.

50mm might be more of a consideration if towing closer to 3500kg limit
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Post Options Post Options   Likes (0) Likes(0)   Quote ofthesea Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar 2020 at 8:22pm
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FWIW the towball size has got nothing to do with fitting to the towbar. There are at least two shaft sizes probably three for ordinary trailers and anyone should be able to get a 50 mm or 1 7/8 ball for around $20 + just need to be sure to get the right shaft size 
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Post Options Post Options   Likes (0) Likes(0)   Quote Bounty Hunter Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar 2020 at 9:48pm
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Originally posted by ofthesea ofthesea wrote:

FWIW the towball size has got nothing to do with fitting to the towbar. There are at least two shaft sizes probably three for ordinary trailers and anyone should be able to get a 50 mm or 1 7/8 ball for around $20 + just need to be sure to get the right shaft size 

yes - youre quite right - the shank+thread size determine the rating of the ball, not the ball diametre 
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