A couple of years ago, I made up a batch of flint knapper/turnscrews to be awarded for prizes, and several of them went out to winners of the ALr postal matches.
I used 1/4" drill rod for the bits: cut them to length, heated the tops in oxy/acet and forged the tip out thin and flared. I then ground them to finished shape, polished them and hardened and tempered them. I like my knapping tool/turnscrew to fit both lock screws, the tang screw and the top jaw screw for the lock, and I file those slots to accomplish that, with a knife file. I case harden lock and tang screws, and top jaw screws these days are usually of tool steel.