Radiator plugs - o-rings, washers or neither?

[candres]

I recently discovered that several of my radiator plugs have been leaking slightly, with varying degrees of corrosion evident, and on inspection I have found that some of the plugs are steel, some are brass and some are chrome-plated.
Not surprisingly the steel plugs have corroded most, but what surprised me was that some, but not all, of the steel plugs have the remnants of fibre washers. On checking suppliers' replacements the chrome plated plugs do seem to come with o-rings but brass plugs do not seem to come with washers or o-rings.

I’d prefer to use brass replacements, to match the existing valves, but should I fit washers?

On fitting replacements I assume I should use PTFE tape on threads but have heard that this can interact with some washers and o-rings.

 

[Kes]

I can't speak for all makes of radiators, but usually the threads in rads are tapered, and require tapered plugs. Steel plugs should not corrode and are perfectly adequate. Use ptfe tape on the threads. Chrome plugs are the worst as the tape will slide on the threads.

If your threads are parallel then you should use parallel threaded plugs with a small flange and a washer or o-ring. Chrome is fine in this context. If you wish you could use a turn or two of ptfe tape around the washer/o-ring, but not on the threads.

Do your existing steel plugs have a flange, or are they all thread? Flange = parallel, thread = tapered.

 

[candres]

Thanks for your advice, Kes.

All my threads and plugs are cylindrical/parallel, flanged.

I had assumed it standard practice to put a few PTFE turns on all such radiator valve threads, threads only, but now I’m confused.

Assuming I can get suitable flanged brass replacements (those I see online appear to have cylindrical/parallel thread sections but have no flange), what type of washer should they be used with – fibre, rubber, leather or plastic?