Attachment 173738
These are wheel studs with a 7/8-14 UNF thread for Volvo trucks, 97mm. in overall length although there are longer ones and other threads. As there would be hell and a half to pay if a truck's wheel falls off, they are probably better steel than many bolts and threaded rods. They are hardened, and so far I have annealed but not machined mine. A file test suggested that they would have been drillable with a carbide drill for sure, and perhaps HSS if a size suitable for the risk of bluntening was suitable. With bolts I have found that a drill slightly undersize, followed by the right one with the corners stoned rounded, gives a finish good enough for bullet sizing. Use of a special gunsmith's reamer would surely require annealing.
The authentic Volvo part may be expensive, but mine are pattern parts, and seem of good quality. They are made from individual forgings, with a forged-in 60 degree centre which isn't as accurate as one drilled on the lathe, but then neither is the loading press to ram alignment in many press and shellholder setups. At a pinch could be used to make your die with a drill press. Prices are still very variable, and at least in the UK this is one of the few things in which I have found eBay a long way from the best deal. It pays to shop around.
I don't believe any kind of loading die really requires the enlarged diameter above the 7/8in. threads, but it looks the part, and the diameter and fine splines give a good grip.