In many places outside the USA and its territories, a different hose fitting thread is used.
The US uses a GHT thread, which is 11.5 TPI (threads per inch), while the UK, its colonial outposts and even some rogue copycats, use the BSP (British Standard Pipe) 3/4" standard, at 14 TPI. See https://en.wikipedia.org/wiki/Garden_hose.
This is a male-to-male adapter to allow the use of US female garden hose accessories, outside that domain.
Why? Well some parts available here on Thingiverse as well as the odd super-cheap garden hose item imported from China, use the US standard. This adapter solves that problem for those of us still stuck in World 1.0.
Designed in Fusion 360. Publicly shared at http://a360.co/2wPCOwe
There's also a Female-to-Female version, at http://a360.co/2wP9rKd
Needs to be printed vertically, such that the threads are horizontal.
If I had continued the 45º chamfers on the hand grip part all the way to the main body, no wasteful supports would have been needed. Use the lightest supports type you can get away with.