If you don't know what a tap & die set is (and there are many who do not): A tap is a hardened steel tool that cuts threads in a drilled hole. (A chart like this will tell you what size the hole should be into which you turn the tap to make various sizes of threads.) A die is a hardened steel tool that cuts threads onto an existing stem. The hexagonal things in this picture are dies. While you can use a die to thread a part that has never had threads, most consumers use a die to rethread a part whose threads have been damaged. (Usually a threaded part attached to something really, really hard to replace!)
Some years ago, my best friend gave me a Black & Decker ratcheting screwdriver set. It was a little orange case that had a ratcheting handle into which you could insert zillions of different bits: all the different sizes of Philips bits; standard screw head bits; hexagonal bits; some that I have never seen before.
If you didn't know that there are different sizes of screwdriver bits--well, I didn't really fully understand this, and why it mattered, until a few years ago. You already know that some screwdriver blades are too thick to go into the screw head. If you insist on using the wrong size bit, sometimes you accomplishing nothing; sometimes you chew up the head of the screw--and then you have drill out the screw, or use a Vise-Grip to grab hold and unscrew it. (Brutal, ugly, and sometimes the head breaks off the screw.)
Anyway, a very nice set. When you put the various bits into the handle, there was a spring loaded ball bearing that held the bit in place with friction. One day several years ago, I noticed that the bits were no longer staying in the handle--just falling right out. The ball bearing was missing--and for the life of me, I can't figure out how it could have stayed there.
I tried to buy a replacement handle--but that didn't seem to be available, and the bits were not the same dimensions as other, similar handles. Even worse: most off them didn't have the neat ratcheting capability. I could buy an entire replacement set (handle and bits)--but these were a bit spendy, and I would have a bunch of bits that were duplicates.
I was looking at this earlier this evening, and I noticed that the little hole in which the ball bearing had resided was .099" diameter. This was just a bit smaller than the hole size you use with a 6-32 tap. (The number 6-32 means a #6 sized screw, with 32 threads per inch.) I grabbed my 6-32 tap, and tapped this hole. Then I turned a 6-32 screw into the hole. Friction between the screw and the bits holds the bits in place just fine, and you don't have to loosen the screw to remove the bit. The only improvement I might make is to replace this conventional 6-32 screw with a 6-32 set screw so that there is nothing sticking out from the side.