(Apologies in advance folks - I'm new to compression fit connections so I suspect this is an obvious question).

I'm preparing to reconnect an old copper tube to my water supply line and refrigerator for the ice maker. Here's what I see at the end that's near my sink:

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The key point that concerns me is that there's no compression nut at all and the compression ring/olive is on there pretty good. I'm not sure how this could have happened but oh well.

My current plan of attack is:

1) Cut off the old compression ring section.

2) Lightly clean the end to ensure there isn't any dirt and debris.

3) Place the compression NUT on first (which seems to come with most water supply valves of appropriate size.

4) Please the compression RING on second.

5) Place the tube in the compression seat of the shutoff valve.

6) Tighten the nut.

Is it really that simple or am I missing something?

I'm confused on a few things:

  • What actually tightens the ring seal to the tubing? Is that done when I'm tightening the nut? Or do I need to apply some sort of glue around the base?

  • Do I need to wrap anything in plumbers tape?

  • How far up the tubing should the ring/olive be? In the old piece, it looks like it was placed about 3/8" to 1/4" up but I'm not sure if that's recommended or not.

2 Answers 2


Yes, quite simple.

  1. use a Scotchbrite pad to shine up the copper tube so the ferrule ring has a clean, gouge free seating area
  2. slide the nut on
  3. slide the ferrule ring on
  4. push the copper tube into the fitting till it seats (fittings I've used have an internal stop at about 1/4" from ferrule seating area, double-check that the fitting is designed this way)
  5. push the ferrule ring into place against the fitting
  6. thread the nut on by hand (make sure the tube doesn't back out of the fitting and till nut is hand tight)
  7. tighten the nut just till the fitting is leak-free (about 1/2 turn from hand tight)

No plumber's goop, no teflon tape on assembly, the seal is formed by compressing the ferrule ring.

Where most people go wrong is to over-tighten the nut for the ferrule ring. The ferrule ring is trapped between two conical surfaces (nut and fitting) that force the ring to bite into the soft copper which both seals and forms a mechanical connection to keep the tube from backing out. Over-tightening causes the ring to dent the tubing, causing leaks and the inability to disassemble and reassemble the fitting as all the give is taken out of the ferrule ring and it cannot compress any more to seal effectively on the next reassembly.

  • In addition: I'd use a copper pipe cutter designed for the job. The sort that clamps on, has cutting wheels and a tightening thumbscrew. They are not very expensive. It may be tempting to use a hacksaw or power tool but these may deform the pipe and not cut at right-angles. I also make sure the cut end is smooth inside and out - 3M sell an artificial wire-wool that I find is very good. May 30, 2014 at 14:15
  • Yes, proper tools for the job on the cut, a tubing cutter is a must, it's quicker and leaves a straight end, superior to the very frustrating hacksaw job (teeth catching, typical angled cut). May 30, 2014 at 14:21
  • I can't get past #6... I can't get the thread to stay on, it's almost as if the ferrule is too big to push deep enough for the thread to mate - but it's an identical (3/8") new connector, so I can't see why that would be the case.
    – Michael
    Jan 20, 2020 at 21:02
  • I have a replacement fitting but its rings look rather dull, should I clean them up too before installing?
    – zzz777
    Sep 27, 2021 at 2:24

Cut the old olive off, then put the new nut and compression olive on. You need to wrap the olive with either PTFE tape or to smother it with jointing compound. Push the end of the pipe into the new compression fitting. Tighten it hand tight, then fully tighten it with wrenches, grips, spanners, etc. As you tighten the fitting, it will crimp the olive onto the pipe.

As long as the pipe is fully pushed home into the fitting, it will crimp the olive onto the pipe at the right point for that fitting.

  • I never put goop or tape on olives in compression fittings, I'm pretty certain they are designed to not need them and it may interfere with the fitting of olive into compression nut. May 30, 2014 at 14:08

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