Mild Steel and Stainless Steel Bolt Specifications

I've been googling this, but I'm hoping someone already with the knowledge can give me some guidance.
I'm getting my old tow bar assembly shot blasted and I'm going to get it galvanised. I want to buy new bolts for it as the current ones could well be 20yrs old and very rusty.
I'm not bothered about them being stainless, though that would be good. Is stainless strong enough? Would I have to ensure they were A70 or a different grade? If stainless is no good is there a grade of mild steel I should ensure I get.
The two bolts holding the ball to the back plate are approx 17mm or 5/8" diameter.
The bolts through the rear cross member and other fixings are approx 12mm or 7/16" diameter.
The smaller ones are M12 thread. I don't have a die big enough to check the 17mm bolts, so I'm assuming the thread is metric.

I can't comment on the other bolts and fixings but the two bolts holding the tow ball on the back plate should be High Tensile Steel.

Check out the last post in this thread for some excellent info.
https://www.landyzone.co.uk/land-rover/high-tensile-bolts-8-8-v-a2-70-stainless.309/

I would use 8.8 or 10.8 steel bolts and replace when surface rust starts to get any depth to it. Stainless looses strength quickly in conditions of repeat loading and a false economy for a towbar.

Fit correct approved bolts / nuts please. Remember your vehicle has the capacity to tow 3500kgs (and is one of the few vehicles left that still can). While you may not tow that much there may be the odd time you may have to or are asked to assist moving something. You don't really want something that heavy detaching whilst on the road. New bolts are fairly cheap,you could always replace them every few years if you want them kept shiny for cosmetic reasons.

brian47 said:

I can't comment on the other bolts and fixings but the two bolts holding the tow ball on the back plate should be High Tensile Steel.

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Cheers, Brian. Thanks for taking the time. I was just wondering if stainless could be had in a form with high enough tensile strength.

Bandit127 said:

Check out the last post in this thread for some excellent info.
https://www.landyzone.co.uk/land-rover/high-tensile-bolts-8-8-v-a2-70-stainless.309/

I would use 8.8 or 10.8 steel bolts and replace when surface rust starts to get any depth to it. Stainless looses strength quickly in conditions of repeat loading and a false economy for a towbar.

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Wow! That's an old thread Stainless is obviously out and I did suspect this would be the case.

Kwakerman said:

Fit correct approved bolts / nuts please. Remember your vehicle has the capacity to tow 3500kgs (and is one of the few vehicles left that still can). While you may not tow that much there may be the odd time you may have to or are asked to assist moving something. You don't really want something that heavy detaching whilst on the road. New bolts are fairly cheap,you could always replace them every few years if you want them kept shiny for cosmetic reasons.

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Cheers, Kwakerman. I do have a small camping trailer which I use quite a bit. However, as you say, it's the occasional times which could be problematic. Every year (except the last 2) I help organise a street fair in the local town. It involves pulling stall trailers which are easily 2 tonne or more, so I need to make sure the bolts are correct. Hence the post and search for info. I can google this, but can you buy approved bolts/nuts? Or, do you need to know the grade such as 8.8 or 10.8 as suggested by Bandit127?

Any caravan centre (or towbar installation places) will have a range of suitable bolts in various lengths (work out what length you need before you go). I think even Halfords do them but only have 1 or 2 lengths available

Kwakerman said:

Any caravan centre (or towbar installation places) will have a range of suitable bolts in various lengths (work out what length you need before you go). I think even Halfords do them but only have 1 or 2 lengths available

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Never thought of a caravan centre
Spot on, I know where there is one just North of Newcastle. Thanks again.

A couple of years ago I was asked by a friend to rescue him after the caravan he was towing had become detatched from his Frontera.
Turned out that he'd used cheapy bolts to fit his towball towing hitch. Yep! the bolts had just stretched and snapped.
His missus drove the Fronty home and as penance he had to listen to me giving a bit of a lecture about using the correct bolts all the way home, from Hereford to Bridgend!

These are 8.8 grade:-
http://www.ebay.co.uk/itm/M16-x-100mm-Tow-Bar-Bolts-Trailer-Caravan-Towing-Hitch-/360302173026?hash=item53e3aedb62:m:mghcPyqq6RB298hQI_2mzhg

Cheers, Brian. I tend to be over cautious anyway, which is why I was asking. I was convinced by you before, but a first hand example does no harm

I'm on ebay myself and looking at these. LINKY as well as others.

You're bolts will be 16mm or 5/8
the min grade I would use is 8.8 a few years ago I worked in a nut not bolt manufacturers made myselfe a set of inconel bolts n nuts should of taken them off the old motor they woz worth more n the landy

brian47 said:

A couple of years ago I was asked by a friend to rescue him after the caravan he was towing had become detatched from his Frontera.
Turned out that he'd used cheapy bolts to fit his towball towing hitch. Yep! the bolts had just stretched and snapped.
His missus drove the Fronty home and as penance he had to listen to me giving a bit of a lecture about using the correct bolts all the way home, from Hereford to Bridgend!

These are 8.8 grade:-
http://www.ebay.co.uk/itm/M16-x-100mm-Tow-Bar-Bolts-Trailer-Caravan-Towing-Hitch-/360302173026?hash=item53e3aedb62:m:mghcPyqq6RB298hQI_2mzhg

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Not only do you need the correct grade, you need the correct type of fixing. Tow bars / hitches are attached with BOLTS not set screws.
This is a problem with ebay which I have fallen foul of myself. Anyone can list anything.

I would also buy a bolt with a recognised manufacturers head stamp. Beware Chinese steel

cooltide said:

I would also buy a bolt with a recognised manufacturers head stamp. Beware Chinese steel

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The way things seem to be going, soon Chinese steel will be all there is!

cooltide said:

Not only do you need the correct grade, you need the correct type of fixing. Tow bars / hitches are attached with BOLTS not set screws.
This is a problem with ebay which I have fallen foul of myself. Anyone can list anything.

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Good point and well spotted, cooltide.
Cheers