Hi Brett,
I'm just creating a materials database from an old Team Lotus designers handbook i have which i'll post here when i have finished it that will give some guidance on materials etc for common uses like bolts, driveshafts etc.
First issue on a double ended bar as you have described is that you will struggle to tighten the nuts up equally as one will turn more easily than the other which will have to bottom out before the other one starts to turn. Might not neccessarily be a problem depending on how well the plain shank is designed as a fit in the u bracket etc.
The preferred method is to use NAS bolts (available as someone said from Trident and other aerospace suppliers). They are basically specified as length of plain shank with a small amount and consistent length of thread on the end, effectively giving you what you desire.
The bolts on the GTD etc are massively over size for the application, which in practicality do give you some margin to use a more standard material bolt cut down as you said without concern. NAS bolts are expensive, probably dozens of times more expensive than the bolts you are currently using, but, probably cheaper and better than trying to make up something special to do the job.
Just for a guide, an F1 car's highest loaded suspension bolt is usually on the front lower wishbone outboard joint (the bolt that holds the lower wishbone to the front upright). This bolt on the cars i designed was 8mm diameter (equivalent to a 5/16" NAS bolt), most of the other suspension bolts were 1/4". An F1 car is about 650kg's ish and over 2 tons at full speed with the downforce. These cars then corner at upto 4g. Our beloved GT40's might be statically heavier but with no downforce and under 1 g corner capability they have nothing like the load in any of the suspension members. So the use of 7/16" ish average to good commerical grade bolts is going to be quite adequate.
D.
