Fit
On my car with the Spax adjustable shocks, I have noted that the bolts are 15/32 in diam (11.9mm), the ID of the bush tube is 12.6 mm so there is approx 0.7mm movement.?
Also the chassis bracket holes for the bolt are 12.2 mm, so another 0.3mm movement.
Shank(shoulder) is only half length of bolt which means half of the bush is on the threads.
At least the bushes fit snugly into the chassis brackets. Inner bush tube and bracket width are same at 38mm.
No guarantee on the measures but were done with vernier.
The bolts are M12 so a nominal 12mm diameter, the bush and bracket IDs are utterly normal clearance holes for M12 bolts thought the slightly smaller size of the bracket holes is likely more to do with the chassis coating than any design decision. Assuming the brackets are parallel and the same distance apart as the length of the bushes then the bushes will be clamped in place properly and there will be no movement of the inner tubes of the bushes. If the bolts are left loose then the entire load will be a shear load on the bolt which is not a good thing regardless of clearances involved or the shank lengths. Incidentally, it would be a nice to have for the shanks to be long enough to span the two brackets so long as they aren't too long and prevent the nuts from drawing up properly which would definitely not be good.
The bolts must be done up tight give an appropriate clamping load; some example quoted figures for M12 grade 8.8 bolts are a maximum torque of 64ftlb (about 86Nm) which gives a tension in the bolt of about 8600 lbf (38.4kN) or about 3.9Te.
It's the friction between the ends of the bushes and the brackets that keeps the bush in place and transfers the loads on the shock absorbers to the chassis, not the bushes bashing against the shanks of the bolts, at least in theory. In practise there will always be some load in shear on to the bolt but this must be minimised, with the tension in the bolt being used to give sufficient friction between the bushes and the brackets.
Saying all that, I've never torqued the bolts, only tightened them by feel to "really quite tight" which is probably somewhere between the figures quoted in the first post (40 to 45ftlbs) and the 64ftlb maximum that I've quoted. Given all the variables inherent in torquing of bolts, particularly those that are a bit awkward to get a socket or crowsfoot on to, I'm not going to worry too much about not getting a torque wrench out. What I have done is sorted out bolts that are long enough for me to get washers under the heads to protect the (now parallel) brackets and that have a little bit of thread projecting beyond the Nylock collars so that they stay tight.
