I've never seen 4-40 thread standoffs (that is the size of the hold down screws for DVI, VGA, serial, etc.), but definitely have seen both 6-32 (aka hard disc screws) and M3 (aka CD-ROM screws ...

shoulder length and the thread length. The screws come in a wide range of shoulder diameters and lengths in both inch and metric sizes. Many manufacturers offer custom or made-to-order screws.

Part of that is probably because we’ve gotten so good at making them that they’re seen as cheap commodities, but the physics and engineering behind the screw thread is interesting stuff.