Pintle hook mounting bolts

[303Gunner]

What grade should the 4 bolts be that mount the pintle to the chassis? Note that I haven't specified the vehicle.

Grade 5 bolts will resist bending and shear forces better that Grade 8, which have a higher Tensile strength. The similar relationship applies to metric Grade 8.8 and Grade 10.9.

So what is needed? Ultimate tensile properties with reduced bending and shear (ie max pulling strength on the hook, but lesser "Ball weight", or adaquate pulling weight and better capacity to bear shear and bending forces from a higher ball weight)?

The reason I have not specified the vehicle is that the Dixon-Bate type Pintle hook as fitted to Australian Army rovers for decades has a much greater pulling and ball weight capacity than the vehicle (or approved trailers) is capable of exerting. But for fitting to heavier vehicles that approach the limits of the hook (4.09t), what monting is appropriate?

[Dervish]

Bolts should never be put under shear stress, and unless in very light duty applications they rarely are. The ball weight and associated up and down forces on the hook are resisted solely by friction between the pintle hook and the chassis; friction provided by placing tensile stress on the pintle bolts.

From memory the pintle hook is mounted with grade 10.9 bolts - it's either that or 8.8, but I'm 90% sure they're 10.9 - for that very reason. Torque applied to the bolts is gargantuan to provide the friction necessary for the job.

[PeteFox]

The bolts on my 6x6 are grade 10.9
Pete

[Chazza]

Interesting post Dervish – thank you! 

I was working on an Isuzu truck at work this week and noticed that the tow hitch has four indentations on the side of the mounting flange. On the tow-bar, four pieces of round bar have been welded on, to correspond with the indentations and therefore supply a rest for the hitch and of course, an aid to resist the shear-force.

It is certainly worth getting this right, because a trailer coming off, must be an absolute nightmare to experience!

Cheers Charlie