How to Measure Thread on SS supply line


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Old 04-09-21, 07:39 AM
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How to Measure Thread on SS supply line

I'm starting to think I'm stupid as I can't find the right adapter to hook up my dishwasher supply line. I thought these things were all NPT, but it's not working for me.

I bought this hose kit:

https://www.homedepot.ca/product/aqu...erm=1000666207

I'm replacing my old dishwasher & supply hose, it runs under the floor and then connects to a 3/8" soft copper pipe (that's 3/8" OD, as I understand). There's currently a compression adapter there but as you can see in my picture - it now leaks. I must have squeezed or jostled it too much with my pliers when I hooked up my new hose.



So I want to replace with a new compression adapter, and I keep buying new ones with MIP ends (tried 5/8", 3/8" and 1/4" MIP) but none of them match. The 1/4" almost exactly matches diameter but the threading looks different from the old adapter that's there now (and the hose won't mate). So I'm guessing the SS hose (female end) is NOT a NPT standard threading??


Help?
 
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Old 04-09-21, 07:59 AM
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Compression threads are not true NPT pipe threads. NPT pipe thread rely on a tapered fit to seal. Compression NPT are a parallel non tapered fit. You need a new adapter.

Let me understand this correctly.
Your water supply line should be 1/4" copper. From there you connect your SS braided hose with a valve (1/4 npt x 3/8 compression) or an adapter 1/4 npt x 3/8 compression. Then to the DW using that special elbow that use to be supplied as standard pars but now you must buy separately (excuse the rant). Again that will connect to your braided hose line using 3/8 "o" compression. Do not over tighten. Hand tight then about 1/8 to 1/4 turn more with wrench.
 
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Old 04-09-21, 08:17 AM
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Thanks Norm201.

My supply line is actually 3/8" copper - at least, I measure it by sliding a 3/8" wrench over the pipe and it fits snugly against it (the outside, of course).

Ah OK so "compression" is also the term to describe the connection size / threading type, not just how the adapter seals against the pipe.

Yeah thankfully the elbow that came with the hose kit fit the dishwasher perfectly, but yes, frustrating that I had to buy it separately.

When you say 3/8 "o" compression - why the "o"? You mean because of the rubber o-ring? Or is "o" compression something different I should also know? :P
 
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Old 04-09-21, 12:29 PM
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My mistake. "O" ring sealing vs. compression ring.
 
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Old 04-09-21, 02:45 PM
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May not be the solution to this issue but I came across a set of these (metric and English) at a garage sale, my god, the best $10 I have ever spent!





 
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Old 04-09-21, 03:09 PM
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Yea if you do enough plumbing you can sort of see what thread you have just by sight. But nowadays I need to double check my "guesses".
 
 

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