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Discussion Starter · #1 ·
Hi everyone,

I attempting to replace a shut off for the first time and have cut the old valve off the nipple... In hindsight probably a bad idea as the Bluefin RVST100 valve doesn't seem to go on well (only turns about 1/3 of a turn on the nipple before stopping). This is described as being FNPT with a MNPT union. The threads on the nipple aren't perfect (some ever so slight signs of corrosion, but nothing looks cross threaded or cut).

The nipple is I'm suspecting IPS. The unthreaded portion measures 1.3270".
First full thread = 1.2775"
Third thread = 1.2975"
5th thread = 1.3050"
With the difference of .0275 I'd imagine this to be tapered (If I measured properly) but it looks straight to my eye.

Have space heaters running and pulled out the caliper and am more thoroughly confused.

From what I can tell the union side on the old valve has tapered (not straight threads) I measure the first thread at 1.7045" and the last thread at 1.735". I can't get a good measure of the female connection on the nipple as it's thoroughly destroyed.

Would be grateful for suggestions on next steps or perhaps product suggestions of valves/fittings to try and open to any pointers.

I don't want to proceed taking the nipple out of the radiator with a spud wrench (just yet) because I think the threading on the new union nipple might be different as nothing else seems to match up.
 

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Discussion Starter · #7 ·
Thanks for all the advice. Happy to say the new valve is on, it's hot with no leaks. I nicked the threads on the inside of the radiator and the new 1" NPT valve was exceptionally right on the nipple but got it on after about 45 mins of cleaning the threads with a file and penetrating oil. Done!
 
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