Radiator Bleed Valve - 1/8-27: Thread Type

[AdamW85]

Morning all. I hope this is the correct place for this post. If not i'll happily move it to another forum area.

I am renovating a property and the old cast iron radiators need a refresh, and i'm going to fit some new bleed valves amongst other things. The female thread in most of the rads could do with a clean out, and some need completely retapping. I'm confident to actually do the job, but wanted to get confirmation on the female thread type beforehand.

The bleed valve itself has a 1/8-27 BSP male thread. It would make sense for the radiator to have a corresponding BSP thread (female). However, a search on google has returned various results, with the female thread in the rad ranging from BSP, BSPT and even NPT.

Is anyone able to shed some light on what the actual thread type is in the radiator please?

 

[exedon2]

Old cast rads will be 1/8 bsp very occasionally 1/4
Re tap with extreme care and pleanty of lubricant very easy to cross thread .

 

[AdamW85]

Thanks. Its definitely 1/8.

Is it BSPP, or BSPT? Given the valves don't bottom out in the rad and seal part way up the thread, I assume it is tapered (BSPT)?

 

[exedon2]

I would certainly expect it to be tapered
I favour loctite 55 rather than ptfe on threads of anything going into cast iron rads

 

[AdamW85]

I would certainly expect it to be tapered
I favour loctite 55 rather than ptfe on threads of anything going into cast iron rads

Ah ok. In the past on bleed valves I have not used any form of sealant/tape, just nipped them up. Never had a problem.

My go to is usually Fernox LS-X on most parallel thread fittings. Might give this a go just to be sure though.