James, I know the type of lathe you need, made plenty of screws myself, but never, ever, could you make a 8 size or a 10 size screw 3/8" to 1/2" in length, with a tool bit. That's why I said you need screw machine lathe that uses acorn dies, usually set up in a turrett post and cuts the same size thread, finishes the head and parts it off.

David