I've used M12 bolts instead of half inch bolts on my wishbone bushes. Is this OK, or will I have problems ?
Any ideas fellas ?

No issues.
You are clamping the bush inner sleeve in the bracket and the level of engineering inaccuracy would not be discernable in use. I use M12 socket head stainless bolts with Nylocs. The bolts are constantly in tension due to the torque, but most of the potentially damaging force is in shear and M12 is huge over-engineering.

M12 would be fine structurally all other things being equal (I've used M10's in fact and I know of others who have used M8's) but I presume you are asking the question because your crush tubes have an inside diameter of 1/2" (12.7mm) and you are worried about the difference?

In my opinion (FWIW) it "should" be okay because the bolt is only there to crush the crush tube and when that happens then the crush tube and suspension bracket almost become one structure. However, I personally would get hold of some 1/2" UNF bolts and nylocs (as I did for my shocker mounts) and fit them to elliminate any doubts. I got mine from Namrick who do mail order. They are probably not the cheapest but for a dozen or so bolts it is not going to break the bank.

If you do decide to use M12's then tighten them up only once the car is on its wheels to ensure that all the slop between the bolts and crush tubes is taken up in the most natural direction.

Cheers,
Craig.

Cheers, yes it was the .7mm slop inside the tubes that was of a concern. Richard at Tiger definately said I should replace them, I wanted a few other opinions !