Parker A-LOK vs Crestflo: Instrumentation Tube Fitting Comparison & Interchange

Parker A-LOK is Parker Hannifin's twin, or double, ferrule instrumentation compression tube fitting. Crestflo builds a dimensionally interchangeable double-ferrule equivalent that's qualified to ASTM F1387, with wider exotic-alloy availability and a 6-8 week delivery on made-to-order work. This page puts the two side by side on design, materials, ratings, standards, lead time and cost. The aim is straightforward: a specifying engineer, an MRO buyer or a distributor should be able to judge the switch honestly before requesting a cross-reference.

These instrumentation compression tube fittings are built for stainless and high-nickel-alloy fluid systems, covering analytical, process, and hydraulic instrument lines. They aren't copper or plumbing compression fittings.

Reviewed by the Crestflo Engineering Team

A-LOK® and CPI™ are registered trademarks held by Parker Hannifin Corporation. Crestflo is an independent manufacturer, not affiliated with, endorsed by, or sponsored by Parker Hannifin. Below, you'll find a comparison provided strictly for dimensional-interchange reference.

What Is a Parker A-LOK Fitting? Twin-Ferrule Design & Catalog 4230/4233

A-LOK is Parker Hannifin's twin-ferrule (two-ferrule) instrumentation tube fitting, covered in Parker Catalog 4230/4233. Two independent ferrules do the work, drawn down together as the nut is pulled up: the back ferrule grips the tube, while the front ferrule forms the primary seal against the fitting body. Parker also builds a single-ferrule version, the CPI™ line; that's a separate product, sealing with just one ferrule. Cross-referencing a single-ferrule connection? Skip this page. Use the dedicated Parker CPI cross-reference instead.

Crestflo makes the matching double-ferrule instrumentation tube fitting. It makes single-ferrule fittings too. Both undergo testing per ASTM F1387, the performance-qualification standard for compression tube fittings, which gives an interchange claim an objective, measurable basis.

Also Known As: A-LOK, Double-Ferrule & Twin-Ferrule Tube Fittings

Buyers and drawings label this fitting family in a dozen different ways. Parker's version shows up as A-LOK, A-LOK fitting, Parker A-LOK, Parker Hannifin A-LOK, Parker A-LOK tube fittings, Parker instrumentation fittings, and under catalog references 4230 and 4233. The broader category goes by double-ferrule tube fitting, twin-ferrule fitting, two-ferrule compression fitting, instrumentation tube fitting, or instrumentation compression tube fitting, depending on who's writing the spec. Crestflo's equivalent carries its own set of names too: Crestflo double-ferrule (or twin-ferrule) instrumentation tube fitting, and Crestflo compression tube fitting. No matter which term your spec uses, the interchange evaluation below still applies.

Design Head-to-Head: Ferrule Geometry, Gaugeability & Tubing

A-LOK and Crestflo both rely on the same two-ferrule grip-and-seal design. A back ferrule hinges and grips the tube OD radially, holding the tube in place and resisting vibration. A front ferrule seals against the body cone. Both systems are gaugeable, too: after pull-up, a gap-inspection gauge confirms the fitting was made up correctly. That means installers can check the connection without taking it apart.

Crestflo supplies ferrules both hardened and non-hardened, built to requirement. That means you can match ferrule hardness to the tubing itself, so the ferrule seats cleanly without galling or biting too deep into the tube wall. It's a small detail, but it matters.

Of course, no fitting works in isolation. Get the best results, and you need instrument tubing that's correctly sized, correctly hardened, and fully annealed, sitting within the recommended wall range for whatever pressure and alloy you're working with.

Parker A-LOK vs Crestflo Specifications Side by Side

When an A-LOK figure shows up only in Parker's own catalog, we cite the source rather than reprint the number. That way, no competitor's value gets misstated. Crestflo figures come from the applicable engineering standard, and they're adjustable to whatever the requirement calls for.

Alloys & Exotic-Material Availability: Where Crestflo Widens the Field

A-LOK comes stocked mainstream in 316/316L stainless, the workhorse instrumentation grade. Select additional alloys are available through Parker as well. What sets Crestflo apart is corrosion-resistant-alloy breadth offered as standard across the double-ferrule fitting range. Each grade below links to its own material page, which explains the alloy and points to the instrumentation forms Crestflo supplies.

Crestflo also supplies Inconel 600/601/718, Monel K500, Hastelloy C-22/B-2/B-3/X, and Nickel 200/201 in instrumentation fitting form. This CRA depth suits chloride, sour-service and high-temperature lines, where a plain 316 fitting just won't hold up. It pairs with NACE MR0175 / ISO 15156 compliance for sour-service selection.

Is Crestflo a Legitimate A-LOK Interchange? The ASTM F1387 Basis

Crestflo fittings are built to swap in dimensionally with the A-LOK envelope, and they're qualified per ASTM F1387, the performance-qualification standard for gaugeable, mechanically-attached tube fittings. F1387 lays out the hydraulic, impulse, rotary-flexure, vibration, thermal-cycle, pull-out and vacuum tests a fitting has to pass. So "interchange" here isn't a marketing claim; it's a measurable, tested equivalence. You can read the standard on the ASTM F1387 interchange qualification page.

Two engineering cautions apply here. First, this reflects a dimensional-interchange and performance-equivalence relationship, not an invitation to mix components. Don't pair a ferrule or body from one brand with a nut or body from another inside the same connection; ferrule geometry and hardness are matched within a system, and swapping parts breaks that match. Second, confirm the exact size and series before you place an order. Crestflo doesn't publish a public A-LOK part-number table. Request a cross-reference instead, and the engineering team will map your specific A-LOK series to its Crestflo equivalent. The Parker A-LOK cross-reference and Parker A-LOK alternative pages handle the lookup and cover the brand-agnostic alternative, respectively.

Certification, Traceability & Testing

Crestflo holds ISO 9001 / 14001 / 45001 and PED certification, plus ASTM F1387 performance qualification for the compression tube fitting line. For sour service work, it meets NACE MR0175 / ISO 15156 requirements. Every part gets a heat/lot number, so full traceability is built in from the start. EN 10204 3.1 material test certificates come standard, and 3.2 is available if you ask for it.

Testing runs deep. Hydraulic proof, burst and impulse, pneumatic, flexure and rotary-flex fatigue, vibration, thermal cycling, pull-out and vacuum: all of it's covered. Positive material identification (PMI) and non-destructive testing happen in-house. Destructive testing, though, goes to ISO/IEC 17025-accredited laboratories. Third-party inspection can be arranged on request.

You won't find certificate numbers listed on this page. Those live in the quality and traceability records instead.

Lead Time, Cost & Buying: A-LOK Alternative Sourcing

Crestflo keeps standard items in stock and builds specials to order, with delivery running 6-8 weeks. Compare that to the 20-plus weeks that's become the norm among major suppliers on many instrumentation lines. Standard product ships from India. When a program calls for domestic melt, though, US or European melt is available on request, complete with full material traceability. Pricing holds up as cost-competitive even after US duties and tariffs. Crestflo also works with small minimum order quantities, and it handles private-label and made-to-print work as well, useful for OEMs, panel fabricators, and distributor line cards. The company is the instrumentation division of an export house that's been in business for four decades, recognized by the Government of India, with a track record of delivery across the Middle East. A well-established supply base, in other words, standing behind a new brand name.

How A-LOK Compares to Swagelok & the Wider Field

Engineers often bring up A-LOK alongside Swagelok and other premium double-ferrule systems in engineering forums. Both carry a solid reputation. As with any two fitting makers, though, components should never be mixed across a single connection. Crestflo isn't looking to disparage either incumbent; the aim is simpler: a tested, interchangeable option that broadens alloy choices and shortens lead times. For a direct comparison with the other major brand, see Swagelok vs Crestflo. Readers wanting the full picture across every brand can consult the master interchange chart.

Products & Request Your Cross-Reference

Crestflo's double-ferrule tube fittings and their nut and ferrule sets are what's being compared here; sizing details sit on the tube fitting size chart. Converting an A-LOK spec is straightforward: request a quote with your size, series and alloy, and the engineering team will send back the Crestflo cross-reference along with a made-to-order lead time. Datasheets and CAD models are available to customers on request. Distributors, OEMs looking for private-label work, and anyone needing samples can reach out through the contact page.

Why Crestflo

Crestflo backs its tested double-ferrule interchange with a breadth and speed most incumbents can't match on exotic-alloy work. The interchange is ASTM F1387-qualified for dimensional compatibility with A-LOK. Its corrosion-resistant-alloy range covers the full spectrum, from 904L and duplex through nickel alloys and titanium. Standard items ship from ready stock, while made-to-order specials arrive on a 6-8 week delivery. Small minimum order quantities, private label, made-to-print: Crestflo handles all of it. Certification runs to ISO 9001, 14001, and 45001, plus PED, with heat-number traceability and EN 10204 3.1 / 3.2 material test certificates backing every shipment. When the specification calls for exotic alloys, a faster turnaround, private label work, or tariff relief, Crestflo is worth a hard look. The company sums up its approach plainly: engineer confidence into every connection.

The Verdict: When to Choose Which

Go with Crestflo when you need exotic-alloy fittings that A-LOK doesn't keep in stock, a quicker made-to-order turnaround, private-label or made-to-print supply, or some relief from US tariff costs. F1387-qualified interchange means the switch carries less risk. Parker A-LOK still holds its ground as the incumbent, though, wherever spec inertia, an established distributor's stock, or a locked approved-vendor list drives the decision. Many buyers running a mixed program keep the A-LOK standard on legacy 316 lines and send new exotic-alloy or long-lead work to Crestflo instead.

Frequently Asked Questions

Related Pages

• Parker A-LOK cross-reference
• Parker A-LOK alternative
• Parker CPI cross-reference
• Swagelok vs Crestflo
• Tube fitting cross-reference hub
• ASTM F1387 interchange qualification
• Double-ferrule tube fittings