Just so I have an on topic post in this thread....lol. Here's some tap holders I made quite a few years ago. I made them to be used in a 12v hitachi hex driver (not impact) that has gone to the big tool graveyard in the sky (actually it's on my workbench waiting for me to get the time to replace the burned out brushes in it if I can).
Top to bottom is 1/4-20 all the way down to 4-40 and it will hold a 2-56. The hitachi was amazingly nimble enough to power tap a 4-40 no problem (If I did my job). 1/4-20 was pushing it sometimes depending on material, and the freshness of the tap, but it was doable (probably what smoked it
). I usually use my 18v makita drill for that, and bigger taps.
I originally made a pile of these blank hex adapters from some 3/8" o1, for a right angle hex driver I had for things like drills and countersinks etc to get into tight places at work. I got the bright idea for these, then made a set. I pursued a patent idea back at the time, but deemed it really not worthwhile (I was broke and didn't have the money to do so....). The small round bit poking out the end was inserted after so they would fit better in my hitachi driver. I've used these also in the right angle driver, and along with 1/4" hex extensions to get into tricky spots (think pulley tap).
It's really just a hole with an intersecting slot the width of your square drive. As you can see on the 5mm on (2nd from top) I had to prick punch the bottom to provide a bit of snap fit on some of them. Otherwise the fit was great, and they don't fall out despite being easy to swap in and out for different taps.
I want to make another set along with a floating holder for my tormach, but just haven't got around to it yet. Same idea, just a different interface.
With the boom of 1/4" hex impact drivers maybe I should pursue selling these to a tap manufacturer. The could not only sell these, but would sell more taps due to people tapping with an impact driver lol.