There are many standards in tech and engineering that are not actually formal standards at all, but for one reason or another, everyone uses them.
There are also many formal standards that seem to have unwritten conventions surrounding them.
This is an attempt to document them, but does not aim to include less common things that are probably not worth anyone's time.
For some reason, this is rhe standard size for many kinds of panel mount switches, USB chargers, etc.
It seems to largely come from automotive and marine. But, if you need a hole in that general size range, might as well make it 1 1/8.
These are the standards for tripods(1/4 is overwhelmingly more common on consumer gear). As far as I know, this is common even in places that use metric, there is no common metric tripod.
This pattern of webbing was invented by the military to securely attach pouches to backpacks and the like. A huge range of accessories are available, and it has become rather cheap in surplus and civilian grade versions.
The 2.1mm barrel plug is extremely common, and more often than not carries 12V DC. However, it also carries other voltages.
Counter intuitively, the female jack is sometimes used to supply power, with short circuit protection.
The jack is very occasionally used for other things like switches as well. Although it is common in consumer gear, it puts a surprising amount of trust in the user not to connect incompatible things, and somehow it seems to work.
In the modern world, however, it seems that USB-C is fast becoming "the standard"
This is rounded, reversible version of USB. Both ends of a C to C cable are the same.
The physical connector is highly reliable. If everything is designed well, it should always be safe to plug anything into anything else, unlike with 2.1mm barrel jacks.
Probably the biggest annoyance for a consumer is that some devices will not charge with a C-to-C cable. You have to use the older A to C, with the big rectangular style on one end for these.