MrPete222 on his YouTube channel posted a series of videos recently about making the subject tap wrench from scratch.
Having broken a tap recently trying to use a cheap hardware store tap wrench, I was interested enough to try building one myself. But, not having knurling tooling or a #12 tap, I decided to tweak the design a bit to use a #10-32 socket head cap screw. I used a bar of questionable steel laying in the junk pile at work, looks like cheap hardware store 1/2" rod, heavily cold rolled. And...it machined like crap, tearing and smearing at any speed/feed combo with fresh carbide cutters...grr! But it polished up pretty nice - a spark test on the grinder showed it clearly has a bit of chrome in it, so maybe not such a crappy choice. My working drawing and a couple of pictures of the final product are shown below.