wanting to replace a radiator and need advice please, my question is I don’t intend to replace any valves as they are relatively new, but the tails in the old rad have a bigger nut than the ones supplied with radiator which have 15 mm stamped on them, so I thought easy option would be to remove old tails and put them in new rad but they won’t budge they are the old type with two lugs on inner.. Can I buy the tails with the larger nut on the tails from anywhere as I cannot see any online. And I don’t want to go to the trouble of replacing the complete valves and draining the system as I am a complete novice at plumbing... Thanks