This is a threaded adapter for a 150mm portable air conditioner hose (common size in the UK), to be mounted to a sheet of plexiglass or in some other ways.

It simply threads inside the hose and creates a good enough seal so hot air won't escape from the hose. I mounted the adapter onto a sheet of plexiglass, then used some velcro (hook and loop) on the plexiglass and around the window frame to achieve a good enough seal.

The holes are for 2.5mm bolts, but you can just use a drill bit to widen them to 3mm or whatever size you have on hand.

I would recommend printing this in PETG, ABS or ASA as the hot air coming out of the AC might warp PLA. I, of course, printed mine in PLA because I'm lazy and that's what I already had loaded.

In theory this could also be used to vent a tumble dryer, if it uses a 150mm vent hose.