Column Style Steel Radiator, difficult to seal threads

Thanks Matt. I try to use a high quality tape and/or dope when I make threaded connections. In this case, I used the Oatey pink tape which is indicated for water, but is quite a bit thicker(perhaps similar to the yellow gas tape) than the slightly cheaper white tape that is common. Other tapes I like include megatape and blue monster tape. But even when I use the cheap white tape, I have enough experience that I never have a problem, it's just a little easier with good tape and worth it to me. After experiencing the difficulties making a good seal, I tried added dope as well as tape, which I have seen can help with a difficult joint. In this case I used Megaloc, which I believe to be a high quality product, and never had a problem with before. Some videos of UK plumbers show a thread sealant product that looks more like a string than a tape. I didn't think it would make a ton of difference where dope was also used, do you think it might?

Ah ok, that's interesting. I did not realize these products were used or recommended to seal plumbing joints. I'm a little hesitant to use the red loctite, since it's possible the radiator may need to be removed for service, or to paint behind it, and heating the joint to 500 degrees F might damage the paint.

A tapered thread on both sides, with a little tape or dope, it works just great. It's not difficult to machine. The connections are pretty forgiving. Do plumbers in Europe really go from job to job hemping and stringing these joints? I honestly don't know, I'll try the product. If that's how it works then fine. But normally I have viewed tape and compound as a helper, or a backup, I thought the threads should mostly seal themselves.

Thanks. Not challenging the need for tape or dope, I always use them. But in this case I used both on parts all supplied by the manufacturer, and I can't seem to get it to seal. I'm a little skeptical the solution could be that string was supposed to be used, but I'm willing to try just about anything at this point.

How does this work, I use the 940 adapter and then sweat in a copper tail? Might work, although I was thinking these below would look better if we think a gasket seal is the way to go, which I'm not sure of. Screwfix doesn't ship to the US, may have to find a shop that does or a friend to help. Was trying to avoid using a grey market part since the radiator is sold in the US, but it might make more sense to use the correct part, than a defective one. Another issue would be maybe needing to re-rough the radiator to make space for the fitting, not sure if that would be the case. The specs say it is "1/2" M Radiator". So what is that? Is it BSP, NPT? Tapered? Something else?

https://www.screwfix.com/p/essentials-1-2-bsp-male-x-15mm-compression-65mm-chrome-radiator-telescopic-valve-extender-2-pack/10954

My limited research seems to agree with that, I read that it is seen as more difficult/expensive to make internal tapered threads than external. Which I interpreted to mean that the male fitting can be threaded too far and it will likely still work, but the internal or female fitting if over threaded won't mate properly. Apparently using a tapered male with a straight female is the accepted solution. And yet, on this side of the pond, NPT fittings mate up just fine every day. I've got the daring loctite 55 on the way, any tips on how to use? I'm a little hesitant to install red or blue liquid loctite, because it may be more difficult to service the joint if I need to. Heating with a torch could damage the paint, and the residual may be difficult to cleanout to re-seal, am I wrong? Thanks for the help.

Oh I that sounds promising. You think there's any chance I'd find a chrome one? How do I connect to this valve and lockshield? It's a compression with a ferrule, probably either 15mm or 1/2 inch. The bottom piece connected succesfully to 1/2" copper tubing.