I Am about to fit a new radiator : the existing pipework that I am teeing off from is 1/2inch . Past experience has told me that I am not going to be able to use a 15mm end-feed tee as it will be too tight. ( I won’t know for sure untill I actually cut the pipe ) it measures 15.10mm My options are the use 1/2 inch to 15mm connectors and then use a 15mm tee . Or just use compression hopefully these will fit, as it’s under suspended wooden floor leaks will not be terminal . I am not asking how to do the job : rather some insight to how the trade would address this job before I make my decision. I am going to wait for warmer weather as I want to change some clapped out rad valves while I have it drained down These are very old so I’m guessing the threads on the valve nut are not going to fit my metric olive puller So may have to cut and snap the the olives off : won’t be able to leave them on as the threads on the nut will not match the threads on the new valves Ps thanks for all the advice on my previous post, regards my sons plastic speed-fit pipework we eventually opted the push on speed-fit fittings : all up and running : very easy I may now be a convert you never know .