You have not told us very much about the application. Of course, the smaller stud is not going to be as strong, and you will lose the benefit of the rolled thread (assuming the existing ones are rolled). Of course, for enough money, you could get them rolled, or set up and roll them yourself (which would be quite an undertaking). Picking up an existing thread is not difficult. The stud material is likely harder (tougher) than something like 1018, but it won't be too hard to cut threads in. I have threaded induction hardened hydraulic shafting - it was hard on the tooling, but doable. I suggest you get the proper form threading tools, then the root radius will be correct - giving you the most strength possible (short of rolling ).