I don't make many, especially nowadays. I had to make them occasionally when repairing instruments, meters etc. It's a fiddly business if you don't do it regula

I don't make many, especially nowadays. I had to make them occasionally when repairing instruments, meters etc. It's a fiddly business if you don't do it regularly and I'm often impatient (it's not something I like doing, it's just a means to an end). Moreover, trying to figure out what the threads are is often pot luck (thread gauges down there are nigh on nonexistent-in my world anyway—and you need a microscope or thread viewing metrology stuff which I don't have). British instruments before, say, 40 years ago usually used BA (British Association), US—UNF and European and Japanese—ISO metric, but then there's also the pre-ISO metric to contend with on old stuff. Surprisingly, when they're that small it often doesn't matter. Guesstimates combined with brute force and ignorance usually got the job done. It's fair to say I'd rarely tackle anything below 0.8mm although I once filed a smaller one by hand. Fortunately, most of the time I scavenge screws from old instruments, clocks, watches and laptop PCs (these however are larger, usually between 1 and 3mm). I never throw away old stuff without disassembling it for the screws. Nowadays, it's not a problem because it's easy to get packs of just about any size screws one wants, it wasn't so 40 or so years ago. Incidentally, my grandfather was a watchmaker and jeweler and my father a mechanical engineer so I saw watchmaker's lathes at a very young age. BTW, my fulltime profession is moving electrons about (or trying to). They're somewhat smaller than those tiny screws so I can only guess where they are by proxy. ;-)