Plug Tube Fittings: Stainless Steel & Alloy Instrumentation Port Plugs
A plug tube fitting is a solid component with a closed end, built for instrumentation compression fittings. It seats into a female tube-fitting port that's not in use, and the nut and ferrule(s) pull it down to a leak-tight seal, so the port carries no flow. Crestflo supplies these port plugs in 316 stainless and high-nickel/CRA alloys, in both imperial and metric sizes. They're dimensionally drop-in and qualified to ASTM F1387, with heat-number traceability on every piece. Standard items ship from stock; specials are made to order, with delivery running 6-8 weeks.
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An instrumentation compression-fitting plug blanks off a female fitting port at its OD-seat. It's not a threaded NPT/BSPT pipe plug under ASME B1.20.1, and it isn't a heat-exchanger tube plug or a plumbing/drain plug either.
What Is a Plug Tube Fitting? Port Plug, Tube Plug & Compression Fitting Plug
A plug is a solid stub, no through-bore, no thread, that slides into the open end of a female tube-fitting port. Tightening the port nut then draws the ferrule(s) down onto the plug's outside diameter, gripping and sealing it just as the same nut and ferrule would seal a length of tube. What you get is an all-metal, gas-tight blank that closes off an unused leg of a tee, cross, manifold or connector. No leak path. No flow.
Buyers specify the same component under several names. This port-termination fitting goes by a tube plug, a tube-end plug, a tube plug fitting, a tubing plug fitting, a port plug, a tube-fitting port plug, a plug tube connector, a compression fitting plug, a compression tube plug, a blanking plug, a solid tube plug, an instrumentation plug fitting, an instrumentation tube plug, or simply a plug fitting. In Swagelok-style catalog logic, it carries a "P" body designator. Whatever the label, it's the same solid instrumentation plug, one that blanks a compression port on its OD-seat.
Plug vs Cap: Which Tube Fitting Do You Need?
The most frequent mix-up is plug versus cap. A plug closes a fitting; a cap closes a tube. Choose a plug when you're blanking off an unused female fitting port, and reach for a tube-fitting cap when you need to dead-end a length of tubing on its OD.
| Component | Seals | Installs on | Typical use |
|---|---|---|---|
| Plug | Inside of a fitting body | Fitting port (nut + ferrule grip its OD) | Blank an unused compression port on a tee, cross or manifold |
| Cap | Outside of a tube end | Tube OD (nut + ferrule) | Dead-end a tube run, cap a stub-out |
How the Seal Works: Single-Ferrule & Double-Ferrule Plugs
A plug seals the same way as any Crestflo compression fitting: the port nut drives one or two ferrules onto the plug's OD to create a leak-tight, metal-to-metal grip with no elastomer in the standard build. As shipped, a plug is a complete assembly, a solid plug body plus the fitting nut and ferrule set (front and back ferrules on a double-ferrule build), so one order gives you a ready-to-install blank. Plugs are offered in single-ferrule and double-ferrule configurations, with hardened or non-hardened ferrules to requirement, matched to the host fitting series. For the trade-off between the two, see single vs double ferrule and hardened vs non-hardened ferrules; for the sealing sub-components see tube-fitting ferrules, single-ferrule fittings and the nut-and-ferrule set.
Plug Tube Fitting Sizes: Imperial (1/16″–2″) & Metric (3–50 mm)
Plugs cover the full compression-fitting range, in both imperial/fractional and metric OD series. They blank off female ports built to accept tube outside diameters up to 2″ (50 mm). Dimensions follow the standard tube-fitting OD tables. Values are set per the applicable standard, and they can be customized to requirement.
| Port OD basis, imperial | Port OD basis, metric | Notes |
|---|---|---|
| 1/16″, 1/8″, 3/16″, 1/4″ | 3 mm, 6 mm | Instrument and sampling ports |
| 3/8″, 1/2″ | 8 mm, 10 mm, 12 mm | General process tees and crosses |
| 5/8″, 3/4″, 1″ | 15 mm, 18 mm, 22 mm, 25 mm | Larger manifold legs |
| 1-1/4″, 1-1/2″, 2″ | 32 mm, 38 mm, 50 mm | Maximum OD |
Common sizes come down to a handful. The 1/4-inch, 3/8-inch and 1/2-inch tube-fitting plugs cover the imperial-fractional side, while 6 mm, 8 mm, 10 mm and 12 mm metric plugs handle the rest. Anyone wanting more detail can check the tube-OD basis, the metric tube fittings page, the imperial-fractional tube fittings page, and the tube-fitting size chart.
Plug Tube Fitting Materials: 316/316L, Duplex, Inconel, Monel, Hastelloy & Titanium Port Plugs
Crestflo carries stainless steel tube plugs in 316/316L, along with duplex, super-austenitic, nickel and titanium alloys. No brass on the US line. The 316/316L stainless steel tube fitting plug serves as the standard SS tube fitting plug on the line, and every 316 tube fitting plug ships with heat-number traceability. Each grade below links to its material page. UNS designations are the standard published references for specification, and bar stock conforms to ASTM A479/A276.
| Family | Grade (UNS) | Grade page |
|---|---|---|
| Stainless | 304/304L (S30400/S30403) | 304/304L |
| Stainless | 316/316L (S31600/S31603) | 316/316L |
| Super-austenitic | 904L (N08904) | 904L |
| Duplex | 2205 (S32205) | Duplex 2205 |
| Super duplex | 2507 (S32750) | Super Duplex 2507 |
| 6Mo | 254 SMO (S31254) | 254 SMO |
| Nickel | Inconel 625 (N06625) | Inconel 625 |
| Nickel | Inconel 825 (N08825) | Inconel 825 |
| Nickel | Monel 400 (N04400) | Monel 400 |
| Nickel | Hastelloy C-276 (N10276) | Hastelloy C-276 |
| Titanium | Grade 2 (R50400) | Titanium Gr2 |
Inconel 600/601/718, Incoloy 800/825, Monel K500, Hastelloy C-22/B-2/B-3/X, Alloy 20, AL-6XN and Nickel 200/201 are all available too, rounding out Crestflo's full material range. Finish options span material finish, electropolish, passivation, silver anti-galling plating and oxygen/UHP cleaning. You'll want to specify cleanliness targets on the RFQ.
Plug Pressure & Temperature Ratings
A plug takes on the working-pressure rating of the tube-fitting system it terminates. A high-pressure port plug, for instance, holds the same rating as the fitting body it blanks. That rating is set by the port OD, wall thickness and alloy under the applicable standard, ASME B31.3 among them. Ratings follow the applicable standard and can be customized to the requirement at hand.
Because a standard plug relies on an all-metal ferrule seal, with no elastomer involved, its temperature limit tracks the chosen alloy rather than a soft-seat rating. Crestflo verifies every plug under its own test regime: hydraulic proof, burst and impulse, pneumatic, pull-out, vibration, thermal cycling and vacuum. PMI and in-house NDT round out the process. Destructive testing happens at ISO/IEC 17025-accredited labs, and third-party inspection is available on request.
Plug Tube Fitting Standards, Certifications & Material Traceability
Crestflo compression plugs are performance-qualified to ASTM F1387, bar stock conforms to ASTM A479/A276, and sour-service builds are supplied compliant to NACE MR0175 / ISO 15156 in the appropriate alloys. The company is ISO 9001 / 14001 / 45001 & PED certified. Every part is marked with its heat/lot number and shipped with an EN 10204 MTC 3.1 as standard, or 3.2 on request.
Drop-In Interchange & Cross-Reference: Swagelok, Parker, Hy-Lok & Hoke Plugs
Crestflo compression fittings meet ASTM F1387, which means a Crestflo plug matches the dimensions of an existing brand's tube-fitting port and drops right in without any redesign. Swagelok® is a trademark of Swagelok Company. Parker® (A-Lok® and CPI™), Hy-Lok®, Hoke®, Fitok® and Gyrolok® belong to their respective owners, and Crestflo has no affiliation with any of them, nor do they endorse Crestflo. We don't publish a part-number table. Instead, our engineers build your interchange list against your exact catalog codes. Request your cross-reference for Swagelok, Parker A-Lok or Parker CPI, Hy-Lok, Hoke, Gyrolok or Fitok. Or start from the cross-reference hub.
Origin, US Service & Lead Time
Crestflo serves the US market, with a sales contact based in Houston, TX. The standard product comes from India, though US or European melt is available on request, and full material traceability comes standard. Need domestic-melt or TAA-eligible material? Our engineering team scopes it as a capability. Fulfillment sticks to the same promise you'll find across the line: ready stock for standard items, made-to-order for specials, and delivery in 6-8 weeks. For details on how that timeline is held, see the lead-time methodology.
Why Buy Plug Tube Fittings From Crestflo
Crestflo is the instrumentation division of an export house with four decades behind it and formal recognition from the Government of India. Deliveries across the Middle East go back a long way for the parent company. That engineering depth now backs a focused instrumentation line built for the US market.
- ASTM F1387-qualified drop-in interchange with the major tube-fitting brands.
- Exotic-alloy availability, duplex, 6Mo, nickel and titanium plugs, not only 316.
- Ready stock for standard items · made-to-order for specials · 6–8 week delivery.
- Small MOQ and private-label / OEM programs.
- Heat-number traceability with EN 10204 MTC 3.1/3.2.
- Both imperial and metric on every fitting. We Engineer Confidence.
Order Plug Tube Fittings: Request a Quote
Send us the port OD, alloy, ferrule setup, and finish. Our team will return a quote with the correct ordering code, kits and mixed-size sets get built to request. Ask our engineers for the ordering-code guide, or configure a part yourself with the part-number configurator from Crestflo.
To request a quote, visit Request a Quote. Need a sample first? Head to Request a Sample. You can also reach the team directly at sales@crestflousa.com or by phone at +1 346 594 9005.
Plug Tube Fitting FAQ
What is a plug tube fitting?
It's a solid compression-fitting plug that seats into an unused female tube-fitting port and seals it leak-tight using the fitting's own nut and ferrule(s), so no flow passes through that port. It has no through-bore and no thread, and it seals on its OD rather than on threads, so it isn't a threaded pipe plug.
What is the difference between a tube plug and a tube cap?
A plug fits inside a female fitting port to close it off; a cap fits over the outside of a tube end to dead-end it. Use the plug for an unused tee, cross, or manifold leg. Save the cap for a length of tubing.
What sizes of tube plug are available?
Port ODs span 1/16″ to 2″ (50 mm) in imperial, fractional sizing, and 3 mm to 50 mm in metric. That's in line with the standard tube-fitting OD series.
What materials can a Crestflo plug be made from?
Grade options include 304/304L, 316/316L, 904L, Duplex 2205 and Super Duplex 2507, plus 254 SMO, AL-6XN and Alloy 20. Inconel, Incoloy, Monel and Hastelloy round out the nickel alloys, alongside Nickel 200/201. Titanium Grade 2 is also available. Brass isn't offered on the US line.
Does a Crestflo plug interchange with Swagelok or Parker plugs?
Crestflo compression fittings are qualified to ASTM F1387 for dimensional interchange. That means a plug drops right into an existing brand's tube-fitting port, no rework required. Send us your part-number cross-reference, and our engineers will match each one to your catalog codes. Swagelok® is a trademark of Swagelok Company. Crestflo isn't affiliated with or endorsed by Swagelok.
Are plugs available in single- and double-ferrule versions?
Yes. Plugs come in single-ferrule and double-ferrule configurations to match the host fitting series, and we supply hardened or non-hardened ferrules depending on what's required.
Are Crestflo plugs NACE compliant for sour service?
Plugs meeting NACE MR0175 / ISO 15156 are available in suitable alloys for sour-service duty. Specify this on the RFQ.
What certification and traceability ship with a plug?
The heat/lot number is marked on every part. Each order ships with an EN 10204 MTC 3.1 as standard, with 3.2 available on request. The company holds ISO 9001 / 14001 / 45001 certification and is PED certified as well.
What is a plug tube fitting rated to?
A plug takes on the working-pressure rating of whatever tube-fitting system it terminates. That rating comes from the port OD, the wall thickness and the alloy, set per the applicable standard. Ratings follow that standard but can be customized to what's needed. Because the seal is all-metal ferrule, temperature limits track the alloy you choose.
Where are Crestflo plugs made and are they TAA compliant?
Crestflo serves the US market as a manufacturer, and its standard product comes from India. US and European melt is available on request, and full material traceability comes standard. When a project calls for TAA-eligible material, that's handled as a scoped capability on request, not a default offering. PED requirements fall under the same approach.
Is a tube plug the same as a threaded pipe plug?
No. This is an instrumentation compression-fitting plug, built to blank a tube-fitting port. It isn't an NPT/BSPT threaded pipe plug, and it isn't a heat-exchanger tube plug either.
Related Tube Fittings & Resources
- Tube-fitting cap, dead-end a tube run
- Nut and ferrule fittings, along with standalone ferrules
- Tee and cross tube fittings, which also carry plug blanks
- Port connector tube fitting
- All tube fittings