This guide shows you what fittings you need to connect up your garden hose to an indoor or garden tap and also how to attach it to spray nozzles, sprinklers, pressure washers and coiled hoses.
The complete guide to garden hose fittings. Commscope Patch Panel
As you're probably aware what's called a faucet in the US and Canada is known as a tap in the UK and the rest of the world. There are also some other regional variants in naming these fittings:
No, it's neither the internal nor external diameter. Thread sizes historically referenced the internal diameter of a steel or copper plumbing pipe that was used with the fitting. For instance a 1/2" BSP thread has an external diameter of about 21 mm or 53/64", whereas 1/2" is approximately equal to 12.5 mm. Pipes historically would have had a thicker wall and 1/2" would have been the inside measurement of the pipe.
Explaining male and female threads.
Tapered threads. One end of the plug is narrower than the other.
Image by Ben FrantzDale, CC BY SA 3.0 via English Wikipedia
Source: National Fire Equipment Ltd.
1 ¹/₁₆" (1.062")
Keystone Jack Module BSP parallel specs. Source: Engineering Toolbox