Proper PEX crimping requires a square cut, the ring 1/8 inch from the fitting shoulder, one full squeeze at 90°, and a Go/No-Go gauge check on every joint.
Learning how to use a PEX crimping tool starts with four non-negotiable parts: a square cut that seats the fitting fully, a stainless steel ring positioned exactly 1/8 inch from the shoulder, one complete squeeze with the tool held at 90°, and a gauge check that confirms the joint is sealed. The process itself is straightforward, but each step depends on the one before it, and skipping any one can leave a leak hidden behind drywall. This guide walks through the exact sequence and the mistakes that trip up even experienced DIYers.
What You’ll Need Before Crimping
Gather everything before you cut the first piece of tubing — stopping mid-job to hunt for a tool is when rushed mistakes happen:
- PEX tubing — must be PEX, not CPVC or copper pipe, which require different fitting systems
- Stainless steel crimp rings sized to match the pipe diameter (½-inch, ¾-inch, etc.)
- PEX crimp tool with jaws that match your ring size; if you are choosing one, our roundup of the best PEX crimping tools covers reliable models for regular use
- PEX tubing cutter for a clean, square cut — a standard pipe cutter can work but the dedicated cutter is more consistent
- Deburring tool or a sharp knife to clean the inside edge of the cut
- Go/No-Go gauge matching your ring size — mandatory for every joint, not optional
How to Crimp PEX — Step by Step
Work through these steps in the order shown. Each step sets up the next, and the sequence is the same whether you are running a new line or repairing an existing one.
- Shut off the water if you are cutting into an existing supply line, then drain the pipe by opening the nearest faucet.
- Cut the pipe square with your PEX cutter. A crooked cut prevents the fitting from seating fully and is the most common beginner mistake.
- Deburr the inside edge of the cut. The plastic burr left by the cutter can push against the fitting barb and prevent a full seal.
- Slide a crimp ring over the pipe end before inserting the fitting. Use the ring size that matches the pipe diameter — ½-inch ring on ½-inch pipe only.
- Push the fitting fully into the pipe until the pipe contacts the fitting shoulder. All barb ridges must be covered.
- Slide the crimp ring up until it sits 1/8 inch from the fitting shoulder, placing it directly over the barbs where the sealing force is needed.
- Open the crimp tool jaws, center them over the ring, and hold the tool square — 90° to the pipe. An off-angle crimp leaves a gap on one side.
- Squeeze the handles completely until they meet or you hear a click. One squeeze, one crimp only. A second crimp work-hardens the steel and can create a leak path.
- Check with the Go/No-Go gauge immediately. The Go side must slide over the ring and rotate freely; the No-Go side must stop. If it fails, cut off the fitting and ring, slide a new ring onto a fresh pipe end, and repeat from step 4.
When the gauge passes, the joint is sealed. No visual inspection can reliably detect an under-crimped ring, so do not skip this step.
Common Mistakes That Cause Leaks
The errors below account for nearly all PEX crimp failures. Knowing them in advance saves you from cutting out a bad joint later:
| Mistake | Why It Fails | How to Fix & Prevent |
|---|---|---|
| Crimping at the wrong angle | Off-angle squeeze leaves a gap on one side of the ring | Keep the tool 90° to the pipe; check alignment before squeezing |
| Double crimping | A second squeeze work-hardens the ring and creates a micro-gap | One crimp only; if unsure, cut off and start over |
| Ring too far from the shoulder | The ring misses the barb ridges; the fitting can push out under pressure | Measure 1/8 inch from the shoulder every time |
| Skipping the gauge check | An under-crimped ring looks fine to the eye but will leak | Use the Go/No-Go gauge on every joint without exception |
| Wrong ring size for the pipe | A loose ring never seals; an oversized ring deforms the pipe | Match ring size to pipe diameter; verify before sliding |
| Crooked pipe cut | The fitting seats at an angle, leaving one barb exposed | Use a sharp PEX cutter; replace a bad cut with a fresh one |
PEX Crimp USA’s official guide includes diagrams that show the same sequence if you want a visual reference alongside these steps.
One last distinction: a standard crimp tool works only with stainless steel crimp rings. If your system uses cinch clamps (the band-style fastener with a screw mechanism), you need a separate cinch clamp tool — the crimp tool will not produce a reliable connection with that ring type.
FAQs
Can I reuse a fitting after cutting off a bad crimp?
If the fitting shows no scratches, cracks, or deformed barbs, it can be reused. Inspect it closely before installing a new ring and pipe — a damaged fitting leaks even with a perfect crimp around it.
What does it mean if the Go side of the gauge will not fit over the ring?
That means the crimp is too tight or the ring is deformed. Cut off the fitting and ring, slide a new ring onto fresh pipe ends, and crimp again. Never force the gauge or attempt to re-crimp the same ring.
Can I use PEX crimp rings on CPVC or copper pipe?
No. Stainless steel crimp rings and standard PEX crimp tools are designed only for PEX tubing. Each pipe material — CPVC, copper, polybutylene — requires its own fitting system and tool type for a leak-free connection.
References & Sources
- PEX Crimp USA. “How to Use PEX Crimp Tools.” Manufacturer’s step-by-step guide for the PEX crimping procedure.