I am ashamed to admit it but I don’t know how to check what size radiator fittings I have (3/4 inch or metric or ????).
What do you measure? The diameter of the pipe supplying the water or the internal bore of the radiator fitting or the diameter of the on the thread or the size of nut that you tighten up.
My specific requirement is to buy a few fittings to seal up some removed radiators (with sludgy water) so that they may be carried, drip free, outside for a flush through.
Edit - I apparently phrased my question incorrectly when doing a search on the internet. I may have found some suitable info.