Superior Fluid Solutions · Cross-Reference
A-LOK® vs Swagelok®: Matching the Ferrule Design Already in Your Line
Parker® publishes A-LOK® as a two ferrule design and CPI™ as a single ferrule design, which makes counting ferrules the first job on any cross-reference.
Before anyone talks about part numbers, somebody has to back a nut off and count. According to Parker®’s own CPI™ and A-LOK® tube fittings catalog 4230/4233, which is a manufacturer publication, the two product families are labelled in the catalog itself as the “A-LOK® SERIES (Double Ferrule)” and the “CPI™ SERIES (Single Ferrule).” Two different arrangements, sold side by side by the same company, which means a drawing naming only a brand has not told you which one is in the line. This post is about establishing the ferrule design that is physically installed and deciding what to do when one line contains both.
Ferrule count is a design difference, not a quality claim
The count tells you how the manufacturer intended the joint to grip and seal. Parker®’s catalog describes the A-LOK® arrangement in terms of a back ferrule, stating that “The Parker Suparcase® back ferrule provides a strong mechanical and anti-vibration hold on the tube,” and describes the CPI™ arrangement in terms of a single ferrule doing that job. Swagelok®’s installer’s pocket guide, MS-13-151, likewise walks through installation in terms of a front ferrule and a back ferrule.
What the count does not tell you is which design is preferable. That depends on the service, the tubing, the vibration environment and what the plant already standardises on, and it is not a question a supplier should answer in the abstract. Nor does a matching count mean parts may be swapped between families or brands. Swagelok®’s pocket guide is explicit on the general point, instructing installers “Do not mix materials or fitting components from various manufacturers.” Counting ferrules is how you describe a line accurately, not a licence to interchange anything.
Three reasons a line’s ferrule design gets lost even in a well run plant.
The drawing names a brand, not a series
A bill of materials that says only the manufacturer name covers two published families with different ferrule arrangements. Nothing on the outside of an assembled joint resolves that ambiguity.
Spares get co-mingled
Loose nuts and ferrules from different series and different eras end up in the same drawer or the same unlabelled bag, and once they are loose the series is no longer readable.
Turnaround work is not always recorded
A joint broken and remade under time pressure often is not written up. Two shutdowns later, the documented design and the installed design differ.
Reading the line: what to look for
Pick a joint that can be safely isolated and depressurised, and follow your site procedure. Back the nut off and look at what comes with it. Count the sealing rings and note the order they sit in along the tube, and whether they are loose or already swaged on from a previous pull-up. Photograph any stamping on the body, nut and rings, and photograph the assembly laid out in order. Then repeat on a second and a third joint, because one joint is a sample of one.
While you are there, capture the rest of the description: tube outside diameter measured with a caliper, wall thickness, tube material and specification, the end connection at each port, and the service medium, temperature and pressure. Parker®’s catalog is a reminder that unit basis also lives in the part number, since it states that metric tube is “designated in millimeters and prefixed ‘M’.”
| What you find | What it indicates | Record this | Do not assume |
|---|---|---|---|
| Two separate rings | A two ferrule arrangement is installed at that joint | Count, order along the tube, any stamping, photograph | That any two ferrule parts from any source will interchange |
| One ring only | A single ferrule arrangement is installed at that joint | Count, orientation of the ring, stamping, photograph | That a single ferrule body will accept a pair of rings |
| Rings gripping the tube tightly | The joint has been pulled up before | Tube condition and length, position of the swage mark | That the tube end can simply be reused without assessment |
| No legible marking anywhere | Nothing about the design family | Caliper readings, thread form, hex size, photographs | The brand or series from the shape of the parts alone |
| Different counts on one line | More than one design family is present | Which joints are which, joint by joint | That the majority design is correct for the whole line |
This table records observations so that a description can be written. It does not map any manufacturer’s parts onto any other manufacturer’s parts, and nothing in it should be read as a statement that components may be assembled across brands or series.
When one line turns out to have both
It happens, and it is not a crisis. Stop treating the line as one thing: log the ferrule count joint by joint and mark the transition points. Then decide, with the responsible engineer, whether the line will be normalised to one design at the next opportunity or kept as it is with the mixed condition documented. Either way, write it down. The cost of a mixed line is almost entirely a documentation cost until somebody orders spares blind.
Keep spares separated after that: label by design family and size, store them apart, and do not let loose ferrules migrate between bins. Superlok® publishes both single and double ferrule tube fitting options, so a description stating the ferrule arrangement, the tube size and the end connection is enough for a Superlok® part to be cross-referenced by form, fit, and function. Superlok® fittings are listed in 316 stainless steel, a corrosion-resistant grade, and Superlok® states that its fittings have the finest interior surface finish of any tube and pipe fitting on the market. Grade, pressure rating and documentation are confirmed per order.
Ordering so the ferrule design stays consistent
Write the ferrule arrangement into the order line rather than leaving it to be inferred from a part number. State it in words, with the measured tube outside diameter and wall thickness, the end connection and thread form, and the service conditions. If you are ordering loose sealing components, say which joints they are for. The shapes themselves are ordinary: ferrule sets, tees, crosses and pipe fittings, plus needle valves where the line needs isolation. For background on how we approach brand comparisons generally, see our cross-reference overview and our post on needle valve manufacturers.
Questions about ferrule design and cross-referencing
Is A-LOK® a single ferrule or a two ferrule fitting?
Parker®’s own CPI™ and A-LOK® catalog labels the A-LOK® series a double ferrule design and the CPI™ series a single ferrule design. Both are Parker® products, which is why naming the brand alone does not identify the arrangement in your line.
Is one ferrule count better than the other?
We do not rank them, and the manufacturer literature cited here does not either. Both are current, published designs. Which one suits a given service is an engineering decision for the plant, informed by the manufacturer’s own ratings and instructions.
Can I put a spare ferrule from one brand into another brand’s body?
No, and we will not advise it. Swagelok®’s installer’s pocket guide instructs installers not to mix fitting components from various manufacturers. Cross-referencing identifies a part by form, fit, and function for a connection. It is not a way to assemble a joint from mixed parts.
Do I have to break a joint to find out what is installed?
Not always. Legible stampings, a surviving bill of materials and caliper readings on the tube will sometimes settle it. When those disagree with each other, or when nothing is legible, inspecting a joint under your site procedure is the only reliable answer.
What do you need from me to cross-reference a part?
The ferrule arrangement in words, measured tube outside diameter and wall thickness, tube specification, body shape, end connection and thread form, service conditions, quantity, and whether documentation is required. Photographs help more than anything else on that list.
Count the ferrules, then talk to us
Send the count, the measurements and the photographs. We will cross-reference from the line as it actually is.
Superior Fluid Solutions
Describe the joint you have, not the joint on the drawing.
Sources
- Parker Hannifin Instrumentation Products Division, “CPI™ / A-LOK® Tube Fittings,” Catalog 4230/4233 (manufacturer publication), supports the labelling of the “A-LOK® SERIES (Double Ferrule)” and the “CPI™ SERIES (Single Ferrule),” the quoted description of the Suparcase® back ferrule, and metric tube being “designated in millimeters and prefixed ‘M’.” parker.com
- Swagelok, “An Installer’s Pocket Guide for Swagelok Tube Fittings,” MS-13-151 (manufacturer publication), supports the front ferrule and back ferrule terminology and the quoted instruction “Do not mix materials or fitting components from various manufacturers.” swagelok.com
- Superlok North America, “Superlok Tube Fittings” product page (manufacturer publication), supports the statement that Superlok® publishes single and double ferrule tube fitting options. superloknorthamerica.com
Technical note: the sources above establish how Parker® labels its own two product families, how Swagelok® describes ferrule installation and mixing of components, and that Superlok® publishes both single and double ferrule options. They do not establish that any part from one manufacturer performs the same as any part from another, they do not establish that components may be assembled together across brands or series, and they do not certify a material grade or pressure rating for your service. Superlok® grade, pressure rating and documentation are confirmed per order.
Trademark disclaimer: Swagelok® is a registered trademark of Swagelok Company. Parker®, A-LOK®, CPI™ and Suparcase® are trademarks of Parker Hannifin Corporation. Superlok® is a registered trademark of BMT Co., Ltd. Superior Fluid Solutions is not affiliated with, authorized by, endorsed by or sponsored by any of these companies, and the marks are used here only to identify the products they name. Cross-references are made by form, fit, and function only.
