Confusing Valve and supply line Nomenclature

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Onespeedbiker

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I am having installed a Roman style bathtub faucet. I have ordered the rough and cover kits. Now I want to get the shutoff valves and supply lines. Currently there are 1/2 copper pipes with compression rings and the rough kit is also 1/2" copper. I would like to maintain 1/2" ID but I am confused by the valve and supply line nomenclature. I understand that 1/2 NOM In with valve means it will attach to the 1/2" copper, but what would be the nomenclature for the supply line out to maintain 1/2" ID and the supply line to connect to 1/2 copper at the faucet line?
 

Terry

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1/2" NOM is OD, I see very few of those stops. We used to use those on dishwashers in the 70's.
1/2" copper pipe is 5/8" OD with 1/2" ID

What brand and model of valve do you have?

supply-line-sizes-terrylove-01.jpg
 
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Reach4

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"Nominal"means what you call/name it. So there can be different things that are nominally 1/2 inch. "1/2 inch" copper is 5/8 inch OD. 1/2 inch tubing is 1/2 inch OD.

May I suggest a digital caliper to help identify what you have?
 

hj

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"nom" means approximate ,i.d., OR, what it "is called". 1/2" nom refers to 1/2" copper, 1.2" steel and brass, CPVC and PVC, BUT ALL OD THESE have different actual i.ds
 

Reach4

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"nom" means approximate ,i.d., OR, what it "is called". 1/2" nom refers to 1/2" copper, 1.2" steel and brass, CPVC and PVC, BUT ALL OD THESE have different actual i.ds
Schedule 40 1 inch refers to more like its ID and 1-1/2 slip joint or 3/8 tubing relates to OD.

1/2 inch compression and 5/8 compression are usually the same thing.

supply-line-sizes-terrylove-01.jpg


I like my description, but I understand there are different ways of looking at it. I think the word nominal derives from the same root as name. A name is what you call it.

In https://www.merriam-webster.com/dictionary/nominal your way is like https://www.merriam-webster.com/dictionary/nominal definition 3b. Strong support for your view and specifically mentions pipe. But I think of it as only loosely related to an actual size. My view is like definition 2a.

But I still think that 1 inch pex or 1 inch schedule 40 or 1 inch tubing or 1 inch compression thread or 1 inch SIDR pipe is really more of a name than an approximation. Yet the derivation of those names were based on approximate size.
 
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Jeff H Young

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It is a little confusing but nominal 1/2 inch copper is 5/8 od just like nominal 3 inch DWV pipe is 3.5 inch od. In my Area all the pipefitters call copper tube out by OD (most of the time) but a plumber never does and you can tell on the job if its a plumber or fitter you work with that way.
I prefer no supply lines sweated copper all the way to the valve
 
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