In my piles of random hardware I have a pile of brass compression fittings for water lines. I have two different types of compression nuts. One has a sleeve inside it. The other doesn't. What's the difference?

Top of nuts Bottom of nuts

2 Answers 2


They both do the same thing except the one on the left has an integral compression ring (ferrule) and the one on the right uses a separate ferrule (which is not in your picture).

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The one on the left tightens the "compression ring" around a (usually copper, but could be plastic) tube. The one on the right tightens itself onto the "coned" (sorta' phallic-shaped) end of a pipe.

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