Fitting TRVs

There used to be at least two different threads on compression nuts for domestic size pipes, but in recent years they all seem to be BSP, I would really expect any domestic radiator valves in the last 15 years or so to be directly interchangeable. ICB, and when I was in a hurry probably would be.

Last year I had to replace a 3 port (CH) valve where the old one was less than 10 years old. The threads didn't match.

At first it did appear to tighten up but I had a small weeping leak. Comparing the old and new treads they appeared to be the same pitch but a slightly different angle. After draining down for a second time and removing the old nut I tried it on the new fitting. It tuned a few times but then just started to bind up on the new fitting.

You can often find dimensioned drawings on the manufacturer's web page.

The original rads in my 1976-built house have 3/4 inch female BSP socket, and the valves were fitted by a Gorilla using boss white and hemp.

That Rothenburger ratchet handle appears to have a female 1/2 inch fitting, whereas all the car ratchets I have seen have a 1/2 (or 1/4, 3/8) male fitting.

I have two types of 1/2 inch ratchet handles that cane with car socket sets.

One has a level to select tighten/undo and has a male fitting.

The other has to be turned over to change the direction and the male 1/2 inch square fitting has to be manually pushed through when the handle is turned over. This "double" male fitting can be removed to leave a 1/2 inch female fitting in the ratchet handle.

However you are correct in that most ratchet handles on sale seem to be of the type with only a male drive fitting where the radiator adapter alone would not fit