Summary

For holding hole-tapping bits.
Cheaper than any other wrench if you only want to get a couple of specifically-sized taps made from good steel.

Instructions

Print out the two parts, heavy infill would be a good idea.
---(Ideally you could cast or machine the pinching block out of scrap metal, though the block might not even be necessary)
Ream out the 8mm hole with a drill bit, or tap it with your bolt itself.
Insert your bolt or studding.
---(Optional step for studding: drill a hole in it and stick something like a pin in it as a handle - pictured for an idea)
Use the bolt to drag an M8 nut into the captive nut slot.
Clamp it onto the square end of a tap, and go cut some threads!