bundy351 is right, basically the same as the cal-track, just building it myself.

tappet, the holes are 12mm and I'll use hightensile, that gives you a shear strength of about 7199kg, doubled because you have two shear faces, it's comes to roughly 14398kg's of force you have to apply before the bolt might shear of. That's not including the clamping force on the sides of the tubes, which now also has to be moved before the bolt shear strength comes into play. Breaking them becomes highly unlikely under these circumstances...

Disclaimer: I worked these things out very quickly, so there might be some errors in my findings...

10.9 = 1040mpa tensile

1mpa = 1n/mm**2

Pi * (r * r)

12mm = Pi * 36 = 113.14285714285714285714285714286mm**2

UTS = 1040 * 113.14285714285714285714285714286 = 117668.57142857142857142857142857n

shear strength = 0.6 * UTS (very rough estimation with some safty in there...)

0.6 * 117668.57142857142857142857142857n = 70601.142857142857142857142857143n

1 newton = 0.10197162129799997 kilogram-force

70601.142857142857142857142857143n * 0.10197162129799997 = 7199.313002634567 kilogram-force

These are just some of the parts we have started making. The bolt part is made out of high tensile allen bolts used to torque down some marine diesel's heads. The two left hand ones have left hand thread, and the right hand ones have right hand thread. The bolts were lathed down to 20mm , and thread cut by my dad on the lathe. The two pieces in the middle is made out of hollow stock which measures 32mm od, and have been machined out to be just larger than 20mm id. The one set of nuts still have to be welded to the tubes, this will enable you to loosen the lock nuts, and adjust these rods any way you want them...

The rings on the end have a 5mm shell, and was lathed out of solid stock, and the rubber mounts that have been pressed in already are rear torque arm bushes for a Jaguar of some kind. Bloody expensive they were.

We will now still have to make the plates to replace the original triangle ones on the front of the leaves, and for underneath the axle.

Some other upgrades are also in the pipeline, but they will be duly noted...