You went under the sink to change an angle stop. The compression nut backed off fine, the valve came away in your hand — and the ferrule is still sitting there on the copper stub, welded on as far as you can tell. It will not slide, it will not turn, and the new valve will not seat over it.
That ring is not corroded on. It is swaged on, and understanding that is most of the job. Here is how to get it off without ruining a stub you cannot easily replace.
Why it is stuck: nothing is holding it but the metal itself
A compression ferrule seals by being permanently deformed. When the nut is tightened, the ring is driven into the tapered seat of the fitting and squeezed down onto the tube until it bites in. The brass flows. It is a cold-forming operation, not a clamp.
So when the nut comes off, nothing releases. The ferrule is now a slightly undersized brass ring sitting on an interference fit it created for itself, often with a visible shoulder of copper raised on either side of it. There is no thread to back off and no adhesive to soften. The only ways past it are to pull it along the tube, split it, or cut the tube behind it.
This is also why they are single-use — a point worth reading in full in the guide to compression ferrule and olive sizing, because the same page explains why the number on the bag will not match the pipe size you think you have.
Decide this first: how much stub do you have?
Everything downstream follows from one measurement. Look at how much copper is sticking out of the wall or the cabinet floor, from the face of the escutcheon to the end of the tube.
- Plenty of stub — you can afford to lose the last inch. Cut the tube behind the ferrule. This is the fastest, most reliable answer and the one I use by default. Skip to the cutting section.
- Short stub — the valve will not have enough tube to grip if you shorten it, or the escutcheon will not cover what is left. Now the ferrule has to come off intact-ish, and a puller is the right tool.
Plumbers get this backwards constantly. They fight a stuck ferrule for twenty minutes on a stub with four inches of spare copper, when two seconds with a cutter would have ended it. Fight the ferrule only when the stub length forces you to.
As an Amazon Associate I earn from qualifying purchases.
The clean way: a compression sleeve puller
A sleeve puller is a small purpose-built tool that does exactly one thing. It captures the tube, seats a jaw behind the ferrule, and then uses a screw to draw the ferrule along the tube and off the end — axial force only, nothing biting on the copper. No cutting, no shortening, no scoring.
WORKPRO 1/2-inch compression sleeve puller on Amazon → — this is the half-inch size, which covers the angle stops under virtually every sink and toilet in a house. It is made for copper ferrules — the listing calls out compatibility with standard 1/2-inch copper compression sleeves.
Two things to know before you buy one. It is size-specific — a half-inch puller is for half-inch nominal copper stub, so check what you actually have before ordering. And it needs a little clearance behind the ferrule to get its jaw in. In a normal under-sink cabinet that is fine. Buried in the back corner behind a disposal, sometimes it is not.
Used properly, the ferrule comes off in one piece and the tube underneath is untouched apart from the shallow ring the bite left. That ring is normal and a new ferrule seats over it without complaint, as long as you are not trying to land the new one in exactly the same spot.
If you work in the trade and want a note when a new guide goes up, leave your email below. No spam, no course funnel — written by a licensed Georgia plumber.
No room for a puller? Split it, carefully
When the stub is short and there is no clearance for a tool, the fallback is to cut the ferrule until it loses its grip, then break it. Done carefully this works. Done impatiently it ruins the tube and turns a ten-minute job into a repipe of the stub.
The method: take a hacksaw blade out of the frame so you can work with it in one hand, and cut along the ferrule — lengthwise, parallel to the tube, not around it. Go slowly and stop before you reach copper. You are not trying to cut through. You are trying to remove enough material that the ring can no longer hold its own compression.
Then put a pair of pliers across the cut and twist. A ferrule that has been relieved along its length will crack open and lift straight off. If it does not, you have not cut deep enough — go back to the blade rather than escalating the force.
Stopping short of the copper is the entire skill. A shallow score in the tube is survivable if it lands where the new ferrule will not sit. A cut that goes through is a leak you will be back for.
What not to do
These are the three I get called out behind, and all three cost more than they save:
- Do not grab it with pliers and twist it off. The ferrule will not turn — but the tube will deform where the jaws bite, and an out-of-round stub will not seal a new compression joint at all.
- Do not pry underneath it with a screwdriver. You will roll a burr up onto the exact band of copper the new ferrule needs to seal against.
- Do not reuse it. If a ferrule does come off whole and undamaged, it is tempting. Re-tightening a used ferrule is the single most common cause of the slow weep that turns up under a cabinet two days later and quietly destroys the base of a vanity.
One more, because the tools look similar enough to reach for the wrong one: a push-fit connector is a completely different mechanism with its own release tool. Removing a SharkBite fitting is not this job, and disconnect tongs will do nothing at all to a swaged brass ring.
If you are cutting the stub instead
Cutting is the default whenever stub length allows, and the only real constraint is space. A full-size cutter will not turn behind a vanity, which is what close-quarters cutters exist for.
RIDGID 101 close-quarters tubing cutter on Amazon → — it swings in a few inches of clearance, which is what you get on a stub coming out of the back wall of a cabinet.
Do not substitute a hacksaw for a cutter here. A sawn end is neither square nor round, and a ferrule cannot seal on either. If your cuts are coming out at an angle, that is a fixable technique problem — see why a tubing cutter cuts crooked.
Before the new ferrule goes on
Cutting raises a burr on the outside of the tube, and the outside burr is the one that matters, because it sits precisely where the new ferrule needs to bite. Take it off.
RIDGID 223S inner/outer reamer on Amazon → — deburrs both faces of the cut.
Then wipe the tube clean and dry, slide the new nut on first and the new ferrule after it, and set the valve. Buy the stop as a kit with its own nut and ferrule rather than sourcing a loose ring — they are matched parts and mixing brands is how a joint weeps. The under-sink shut-off valve picks covers which stop to fit, and if you are weighing whether to stay with compression at all, compression against push-to-connect is the honest comparison.
Frequently asked questions
Can you reuse a compression ferrule if it comes off undamaged?
No. A ferrule has been permanently deformed to the shape of one specific joint at one specific depth, so even an undamaged-looking ring will not re-seat reliably. Re-tightening a used ferrule is the most common cause of a slow weep that appears days later.
Do you have to remove a stuck ferrule at all?
Only if the stub is too short to cut. If there is spare copper coming out of the wall, cutting the tube behind the ferrule is faster and more reliable than any removal method.
Will a compression sleeve puller damage the copper stub?
It should not. A puller applies force along the tube rather than gripping across it, so the copper is left with only the shallow ring the original ferrule bit into, which a new ferrule seats over without a problem.
What size sleeve puller do you need for an angle stop?
Half-inch nominal covers the stops under nearly every sink and toilet, but pullers are size-specific, so confirm the stub you actually have before buying one.
Related guides
- Compression ferrule sizing: match the tube, not the pipe
- Best under-sink shut-off valves
- Compression vs push-to-connect valves
- Toilet supply line size
Fix the 12 Most Common Plumbing Problems Yourself — Free Plumber’s Handbook — including how to stop a leaking pipe before it floods the room
Step-by-step fixes for the 12 most common problems — and exactly when to call a pro. Free and instant, from a licensed plumber. Save hundreds on calls you didn’t need.