3/4" unions with different size threads?

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Old 10-21-12, 12:31 PM
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3/4" unions with different size threads?

Hi all.

I'm moving and resizing some Baseray cast iron baseboards and found something strange.

The baseboards have 3/4" male unions and I have a valve and a union elbow - both 3/4" and only one will fit! I thought they should all be standard NPT threads. You can see it in the pics.

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I was going to buy a new union elbow and valve, but I don't know if they'll fit! I could replace both sides of the union, but I don't know how to remove the radiator side. There's nothing to grab on to. What tool would I use?

Any idea of what's going on? There's no doubt they're different size threads (very close though).

Thanks.
 
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Old 10-21-12, 12:54 PM
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The threads that join two union halves are not standard.
If you wanted to use any part of an old union you would need to somehow transfer the half you wanted to move.
They are proprietary for the manufacturer that made them.

The part with the nut that is attached to the radiator could be soldered, brazed or threaded.
If threaded there could be a hex or square inside the fitting that you could catch with an Allen wrench or ratchet.
 
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Old 10-21-12, 01:09 PM
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Thanks Greg.

There's nothing to grab on to. When you pull the nut all the way out, it's all round. Not flat side for a wrench.

The radiator has 'standard' 3/4" threads. I guess I'll just have to figure out a way to remove the radiator side and start from scratch
 
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Old 10-21-12, 02:01 PM
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The radiator side most likely has a pair of ribs or tongues inside. You need a radiator valve "spud" wrench to fit inside the fitting and it meshes with the ribs and then you use a regular pipe wrench on the spud wrench.

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