On 08/11/2019 11:40, T i m wrote:
On Fri, 8 Nov 2019 03:18:08 -0800 (PST), wrote:

On Friday, November 8, 2019 at 11:12:09 AM UTC, T i m wrote:
On Fri, 8 Nov 2019 02:16:35 -0800 (PST), wrote:

On Friday, November 8, 2019 at 10:12:17 AM UTC, wrote:
Is the connection between a radiator tail and the actual valve any sort of standard?

This bit is a stupid question isn't it. It must be either 3/4 or 1/2" because why would anyone bother setting up for anything else.

I think you have missed the point of the question by snipping and only
replying to one bit (missing the 'bigger picture' in the process).

Not quite, because I replied to my own question!

Doh! ;-)

It wasn't the diameter of the input pipe,

I was referring to the size of thread that connects the valve to the tail, and realised that surely no one would make it anything other than 3/4 or 1/2, so if it looks like a 1/2, it is a 1/2.

Well, I'm not sure you can even assume they will be interchangeable,
even if they are nominally the same size / type of fitting.

I say that because I have gone to replace say a gate valve and hoped
to retain the existing nuts / olives, only to find the thread a
different pitch / tightness?

it was the distance between
that pipe and the radiator, something someone replacing a std with a
complete new TRV would like to know.

That question stands.

I think has been answered elsewhere. I think with my experience with
plumbing, unless you are replacing exact like for like, there is a
good chance that something will be different (and rarely in your
favour). ;-(

I have certainly found in the past that things were not interchangeable
- even nuts from one compression fitting to another - but everything I
have used in recent years has been (replacing gate valves with lever
ball valves, straight couplers with isolation valves and the like).
Maybe manufacturers used their own standards in the past, but these days
do stick to standard lengths and threads?

SteveW