I was helping a friend who is building something which uses a heat exchanger to heat the air. He bought a heat exchanger which is meant to be part of an outside split aircon unit I suspect. It's got what looks like a 28mm copper input and output (which fans out into lots of microbore going through the fins).
However, on connecting, it was larger that 28mm. Ah, maybe it's 1" imperial? Nope, larger than that. It's 1⅛" ACR pipe. (ACR = Aircon and refrigeration, which still works in inches, but not same as the imperial sizes.)
So I was amused by the variety of almost-28mm copper tube sizes:
28mm - standard for water and gas.
28.24mm - 1" imperial which was standard and I still find in use.
28.65mm - 1⅛" ACR pipe for aircon and refrigeration.
To connect to 15mm copper for feeding water through it, I eventually suggested 1⅛" ACR to ⅞" ACR (which is 22.225mm) to connect 22mm pipe, and then a bog-standard 22mm to 15mm adapter.
Initially we talked about using a swaging tool to generate a 1⅛" ACR socket in 28mm copper tube, but they're expensive. He knows some aircon companies, and none had a swaging tool that large - probably need a company which does datacentre or supermarket fridge/freezer cabinet installs to be using 1⅛" ACR copper tube.