Suzuki 4WD Club of Victoria

That's much more professional than any official advice I will be seeking thanks Mike.

I think I will reinforce where I bolt it in with a bit of extra steel, not sure if I will go a total of 9mm but I will try go more than the 13mm of steel to back it up.
your point about the shackle being the weakpoint is pretty poinient in the fact that I will probably only ever be using 3.25.

Hi Jon

The point about the pin size was that I can only rate my tow point at 5 tonnes if I use a shackle with 23mm dia pin. They don't exist so I use a 19mm dia pin and then the formula no longer applies. A shackle with a 23mm dia pin will have a significantly higher rating than any of us will ever need. But if you are using the formula to calculate the situation where you have a correctly fitting bolt through a whole then the formula is applicable. Sorry if my example might have been a bit confusing. The point is that the bolt or pin cannot be a lot smaller than the whole or the formula does not apply.

Mike

I understand.
the surface area of a small pin is putting strain on a smaller point in your steel work so that steel work is more prone to breakage and excitement.

Yes, that is correct.