1 Original bits
2 Bits with holes
Got caught outside without tools once too many times. Given that the size of the exchangeable bits for screwdrivers is so small, and when they are needed they are sorely missed, finding a way to have them always available became crucial.
Because facing a problem and not having at least improvised tools is a ROYAL pain. You do not want to go out without a screwdriver.
First we buy suitable screwdriver tips ("bits"). We intentionally aim for the cheapest sort, made of cheap nontreated steel (picture 1; higher quality quenched steel is difficult to drill; the bits will be prone to quick wear, but we don't expect daily use anyway). We drill a 4mm hole into each bit we think we will need (picture 2, in this case it was one flat and one Philips, the sizes for bolts most commonly found in computer equipment). We cut the burrs, and put the bits on the keyring. We're done.
4mm hole is a bit tight fit for the keyring used. Bigger would be better, but the equipment used did not allow accuracy high enough for a bigger hole. An attempt to drill a 5mm hole failed.
Find out how to drill holes into hardened steel. Do the same with higher-quality bits.