Reducer Tube Fittings: Stainless Steel & High-Nickel Alloy

A reducer tube fitting joins two instrumentation tubes that don't share the same outside diameter, stepping the line up or down while keeping a gauge-able, leak-tight double-ferrule seal at each end. It's the fitting you reach for when an impulse line, a sample line, or a gauge hookup needs to move between two tube ODs. No weld required. No thread transition either.

Crestflo manufactures reducer tube fittings in stainless steel, high-nickel alloys, and titanium, with end connections up to 2" (50 mm) OD, in both imperial and metric sizes, tested per ASTM F1387 for dimensional interchange with the major compression-fitting brands. Ready stock for standard items, made-to-order for specials, 6–8 week delivery. Request a quote or request a free sample.

> Scope: an instrumentation tube-fitting reducer that steps between two tube outside diameters. It's not a pipe reducer, concentric or eccentric, an HVAC or duct reducer, an electrical reducer, or a pressure-reducing valve.

Reducer Tube Fitting Also Known As: Tube Reducer, Reducing Union & Port Reducer

Across specifications and purchasing systems, engineers call this same part by several names. A reducer might show up as a tube reducer, reducer tube fitting, tube fitting reducer, or tube reducer fitting. The two-fitting-end variant goes by reducing union, reducing union tube fitting, or tube reducing union. You'll also see related terms: tube end reducer, reducing connector, size reducer fitting, tube size reducer, port reducer, and bore reducer. In tube-fitting purchasing, people sometimes call it a reducing bushing (tube-fitting sense), loosely, though the true bushing is a threaded-pipe part. A reducer always joins a larger tube to a smaller one through a ferrule grip, so depending on the seal design, it's also described as a compression tube reducer, a single-ferrule reducer, or a double-ferrule reducer.

How a Tube Reducer Works: Double-Ferrule Grip & Seal

A reducer is just a short, straight body, bored straight through, with a tube-fitting connection on each end. Each connection relies on a nut and ferrule set. Pull the nut up, and the ferrule advances, swaging onto the tube surface. That action does two things at once: it forms a mechanical grip that resists blow-out, and a metal-to-metal seal that contains the fluid or gas. There's no elastomer in the seal path, so the joint holds up across whatever temperature range the base alloy allows.

Crestflo makes both single-ferrule and double-ferrule fittings, with hardened or non-hardened ferrules available depending on what the job calls for. Every part carries a heat/lot number, so full traceability is never in question.

Want to see how the seal actually comes together? Check the nut and ferrule and single-ferrule pages. To weigh the two designs against each other, look at single vs double ferrule.

Reducer vs Reducing Union vs Port Reducer: Which Type You Need

Tube reducers split into groups based on how each end terminates. Every one of them is concentric. That familiar concentric-versus-eccentric distinction isn't theirs to claim; it belongs to pipe reducers, not instrumentation tube fittings.

For an equal-size tube-to-tube join, use a union or connector instead; for a tube-to-thread transition (NPT/BSP/SAE), use an adapter. Browse all tube fitting types for the full range.

Reducer Sizes: Imperial (1/16"–2") & Metric Tube ODs

Instrumentation reducers cover tube ODs up to 2" (50 mm), available in both imperial fractional and metric systems. They can pair almost any two sizes, adjacent or not. Common instrumentation size-pairs appear below; all sizes follow standard OD tables and can be adjusted to fit specific requirements.

Metric-to-imperial reducers are also made to order. Confirm the full range on the tube fitting size chart, tube OD reference, metric tube fittings, and imperial-fractional tube fittings.

Stainless Steel Tube Reducer Materials: 316/316L, Duplex, Inconel, Hastelloy & Titanium

Reducers come in the same corrosion-resistant alloys as the rest of the compression-fitting range, so you can match the fitting to the media and the service. The 316 stainless steel tube reducer handles most instrumentation work; it's the grade to reach for first. Specify a 316 tube reducer for general fluid and gas lines. Chloride exposure, sour service, or high temperatures call for something more, so step up to a duplex, nickel-alloy, or titanium body instead. Each grade is supplied to its own bar and tube standards: stainless to ASTM A479 for bar and ASTM A269 for tube, nickel alloys to whichever ASTM B-series bar standard applies to that grade (Inconel 625 to B446, Inconel 718 to B637, Incoloy/Inconel 825 to B425, Monel 400 to B164, Hastelloy C-276 to B574), and titanium to ASTM B348. Mill test certificates come with all of them.

Crestflo only offers these grades as instrumentation fittings, valves, and tubing. Need deeper alloy options for reducers? Check the matrix pages for Super Duplex 2507, Duplex 2205, Inconel 825, and Hastelloy C-276, or browse all materials instead. Finishes on offer include material finish, electropolish, passivation, and silver anti-galling plating.

High-Pressure Reducer Ratings: Pressure & Temperature

A reducer's working pressure is set by the smaller of its two tube ends - that end's OD and wall thickness - together with the base alloy. This follows standard tube working-pressure tables built from ASME B31.3 allowable-stress values, the same ones Crestflo works from. A high pressure tube reducer earns its rating from that heavier-wall smaller end, so specify the smaller OD and wall for whatever pressure class you need. Temperature capability, by contrast, tracks the alloy: the double-ferrule joint seals metal-to-metal, and there's no elastomer anywhere in the flow path. Values follow the applicable standard and can be tailored to your requirement.

Size the pairing with Crestflo's tube pressure & wall-thickness calculator. Then check pressure, temperature derating before you specify.

Standards, Certifications & Traceability

Crestflo manufactures every reducer under a quality system certified to ISO 9001 / 14001 / 45001 & PED. Each unit also carries the standard approvals for compression tube fittings. Certificates? They're posted in the quality section.

Testing covers a lot of ground: hydraulic proof, burst and impulse, pneumatic, flexure and rotary-flex fatigue, vibration, thermal cycling, pull-out, and vacuum, all backed by PMI and in-house NDT. Destructive testing takes place at ISO/IEC 17025-accredited labs. Third-party inspection is available on request as well. For the full technical detail, consult the standards directly: ASTM F1387, NACE MR0175, ASTM A269, ASTM A479, and EN 10204 MTC.

Swagelok, Parker A-Lok, Hoke, Hy-Lok & Fitok Reducer Interchange

Crestflo reducers are dimensionally interchangeable equivalents for the major brands, qualified per ASTM F1387 rather than left to a catalog claim. The same body serves as a drop-in Swagelok® reducer, Parker A-Lok® reducer, Hoke® reducer, Hy-Lok® reducer, and Fitok® reducer, matched on ferrule geometry and thread rather than swapped by catalog number alone. Swagelok®, Parker®, A-Lok®, Hoke®, Hy-Lok®, and Fitok® are trademarks of their respective owners; Crestflo is not affiliated with, endorsed by, or a licensee of any of them, and no genuine-brand parts are supplied. For a size-by-size match to your current part numbers, request your Swagelok® or Parker® cross-reference from our engineering team, or start at the cross-reference hub for Hoke, Hy-Lok, and Fitok equivalents.

How to Order a Reducer & Specify Your Part

To spec a reducer, give the two tube sizes and the service: End A OD × End B OD × alloy × ferrule (single or double, hardened or non-hardened) × finish. Our engineering team sends back the matching configuration and lead time. Datasheets and CAD models are available to customers on request. To request the ordering-code guide or place an inquiry, request a quote or request a sample from Crestflo.

Why Crestflo for Reducer Tube Fittings

Crestflo is the instrumentation arm of an export house that's been in business for four decades, recognized by the Government of India, with a solid delivery record across the Middle East. Now it's built out for the US market. That history stands behind a supply model aimed at specifiers who need something that actually drops in and works, not just on paper.

• ASTM F1387-qualified drop-in, interchange proven by test, not asserted.
• Standard items ship from ready stock. Specials get made to order, with delivery in 6 to 8 weeks. Compare that to the 20-week-plus lead times typical of the majors.
• Indian origin; US / European melt available on request, with full material traceability.
• Small MOQ and private label for OEMs and distributors.
• Both imperial and metric on every size-pair, cost-competitive after US duties.

Confidence is what we engineer at Crestflo. Take a look at our lead-time program, our private-label capability, our material traceability, and our US origin compliance.

Reducer Applications in Instrumentation Systems

Reducers show up anywhere a tube run steps down or up in diameter. That includes impulse and sample lines, gauge and transmitter hookups, analyzer and grab-sampling systems, instrument air, hydraulics, and steam-tracing loops. You can see where they fit across industries. For inquiries, go through our distributor program or reach us via the contact page.

Reducer Tube Fitting FAQ

Related Tube Fittings & References

• All tube fitting types
• Union tube fitting, equal-size join
• Port connector
• Adapter tube fitting
• Tube fitting size chart
• Swagelok cross-reference
• Why Crestflo

Reviewed by the Crestflo Engineering Team