Fitting radiator vales to the radiators, help please

[happyhero]

Hi I have fitted the odd radiator in the past but I cannot remember this part from before so I can't think what I did about it.

Basically I have bought a small towel radiator for our downstairs toilet and a couple of valves, one of which is a TRV4 thermostatic valve. They both have little stubs, don't know what their proper name is but the bits you screw into the radiator that the valves tighten onto.

My question is with these threaded stubs, I cannot see what stops you from screwing them in until they are inside the radiator, I tried with my hands and they seem to stop where you would expect but I am guessing a spanner would just keep driving them in. There does not appear to be any shoulder inside the rad to stop them and the stubs don't seem to have any part on them that will hit and stop them, although amazingly they do stop hand tightening them. Can anyone explain what happens here?

Also how many turns of PTFE tape do you need here?

Do I tighten them quite hard with a spanner or is it the tape that is supposed to stop any leaks?

I don't want to over tighten them if they are just supposed to be tight due to a few turns and the tape.

Any advice or help appreciated

 

[kbdiy]

In my experience much depends on the quality of the threads in the rad or towel rail as to how much PTFE tape is needed. I generally go for about 6 turns and tighten as much as seems necessary when resistance is met. If you don't feel enough resistance then remove the tail and wrap more tape around it.

I recently replaced valves on all my rads (10 rads so 20 tails to insert) and had no leaks at all on any of them.

 

[Charnwood]

There are 2 types of tail.
Most are tapered and will tighten up part way along the thread.
Some (rare as RHS) are parallel and will have a shoulder and seal.