Tube Fitting Size Chart: Imperial & Metric OD Dimensions
A tube fitting size chart is a single reference table. It lists the tube outside diameters, or OD, that an instrumentation compression fitting is built to grip, given in both fractional-inch and millimeter, along with the imperial-to-metric equivalents you need to size a part, cross-reference it, or order the correct one. Crestflo instrumentation tube fittings run from 1/16" up to 2" (50 mm) in the fractional-inch series and from 2 mm through 50 mm in the metric series, sized by tube OD, available in single or double ferrule, and made in stainless and high-alloy grades. This chart doesn't cover everything, though. It's limited to instrumentation stainless-steel and alloy compression tube fittings, not AN or automotive (SAE J514 dash-size) fittings, and not copper or plumbing compression fittings.
Request a quote at crestflousa.com/request-a-quote. Standard items ship from ready stock; specials are made to order, with delivery running 6 to 8 weeks.
Also Known As: Tube Fitting Dimensions, OD Chart & Compression Fitting Size Table
Engineers name the same reference a dozen different ways on drawings, RFQs and buying notes. Some ask for tube fitting sizes, tube fitting dimensions or tube fitting standard sizes. Others want a tube fitting dimension chart, a tube fitting size table or a tube fitting size guide. Still others call it a tube fitting OD chart or tube OD chart, or a compression fitting size chart and compression tube fitting sizes. Then there's the material- or configuration-specific crowd: stainless steel tube fitting sizes, stainless steel tube fitting dimensions, a steel tube fitting size chart, instrumentation tube fitting sizes, and double-ferrule or single-ferrule fitting sizes. Every one of these points to the same thing: the tube-OD sizing system for instrumentation compression fittings, given in inches and millimeters.
How Tube Fittings Are Sized: Tube OD, Not ID or Thread
Instrumentation tube fittings are sized by the tube's outside diameter (OD), the surface they actually seal against. Not the inside diameter. Not the end thread. A 1/4" fitting grips 1/4" OD tube, and a 6 mm fitting grips 6 mm OD tube. Measure the OD with a caliper or an OD tape, then match the fitting to that number. It's the ferrules that grip and seal the tube, not how hard you tighten the threads. Crestflo's guide on ferrule installation and gauging explains how the pull-up gets set and checked. The OD figures listed below come from the standard published tube-fitting dimensions, though fittings can be customized to whatever the job requires.
Tube Fitting Size Range: Imperial & Metric OD (1/16″–2″ · 2–50 mm)
Crestflo puts the full tube-OD ladder, in both measurement systems, on every fitting, starting with stainless steel and running across the whole alloy range. The size list doesn't shift by alloy: the same OD series shows up in 316/316L right through the high-nickel grades. Material changes rating and price. It doesn't touch the size. Where a discrete size has its own product page, you'll find it linked in the tables below.
Imperial (Fractional-Inch) Tube Fitting Sizes in Inches
| Tube OD (in) | Decimal (in) | Per-size page |
|---|---|---|
| 1/16" | 0.0625 | — |
| 1/8" | 0.125 | 1/8 inch tube fittings |
| 3/16" | 0.1875 | — |
| 1/4" | 0.250 | 1/4 inch tube fittings |
| 5/16" | 0.3125 | — |
| 3/8" | 0.375 | 3/8 inch tube fittings |
| 1/2" | 0.500 | 1/2 inch tube fittings |
| 5/8" | 0.625 | 5/8 inch tube fittings |
| 3/4" | 0.750 | 3/4 inch tube fittings |
| 7/8" | 0.875 | — |
| 1" | 1.000 | 1 inch tube fittings |
| 1-1/4" | 1.250 | — |
| 1-1/2" | 1.500 | — |
| 2" | 2.000 | — |
Crestflo's smallest fitting comes in at 1/16" OD, and the largest tops out at 2" (50.8 mm) OD. Check out the full imperial / fractional tube fittings line for the complete range.
Metric Tube Fitting Sizes in mm
| Tube OD (mm) | Per-size page |
|---|---|
| 2 mm | — |
| 3 mm | — |
| 4 mm | — |
| 6 mm | 6mm tube fittings |
| 8 mm | 8mm tube fittings |
| 10 mm | 10mm tube fittings |
| 12 mm | 12mm tube fittings |
| 14 mm | — |
| 15 mm | — |
| 16 mm | — |
| 18 mm | — |
| 20 mm | — |
| 22 mm | — |
| 25 mm | — |
| 28 mm | — |
| 30 mm | — |
| 32 mm | — |
| 38 mm | — |
| 50 mm | — |
This metric tube fitting size chart spans 2 mm to 50 mm OD. For the complete lineup, see the full metric tube fittings line. Every measurement here follows tube OD as the standard.
Fractional-to-Metric Tube Fitting Size Conversion (Inch to mm)
The inch-to-millimeter equivalents below use the exact factor of 25.4 mm per inch. Treat them as reference only. A fractional-inch OD almost never lands on a whole-millimeter OD, and imperial and metric fittings are not interchangeable. A 1/4" fitting (6.35 mm) won't seal on 6 mm tube, and a 6 mm fitting won't seal on 1/4" tube, so choose one system per tubing run.
| Fractional (in) | Decimal (in) | Exact mm (× 25.4) | Nearest metric fitting (not interchangeable) |
|---|---|---|---|
| 1/16" | 0.0625 | 1.59 | 2 mm |
| 1/8" | 0.125 | 3.18 | 3 mm |
| 3/16" | 0.1875 | 4.76 | — |
| 1/4" | 0.250 | 6.35 | 6 mm |
| 5/16" | 0.3125 | 7.94 | 8 mm |
| 3/8" | 0.375 | 9.53 | 10 mm |
| 1/2" | 0.500 | 12.70 | 12 mm |
| 5/8" | 0.625 | 15.88 | 16 mm |
| 3/4" | 0.750 | 19.05 | 20 mm |
| 7/8" | 0.875 | 22.23 | 22 mm |
| 1" | 1.000 | 25.40 | 25 mm |
| 1-1/4" | 1.250 | 31.75 | 32 mm |
| 1-1/2" | 1.500 | 38.10 | 38 mm |
| 2" | 2.000 | 50.80 | 50 mm |
For picking the right system, take a look at metric vs imperial tube fittings.
Tube Fitting Nut, Hex & Wrench Size Reference
The nut's hex across-flats, and with it the wrench size, grows as the tube OD grows. The exact figure isn't fixed by any public standard, though; it depends on the fitting series and the ferrule design. A wrong wrench-size table means rounded nuts out in the field. That's why Crestflo publishes the certified hex across-flats, in both inches and millimeters, for each size right in the ordering guide, rather than relying on a generic chart. Ask our engineering team for the hex/wrench reference covering your size range, and include it with your RFQ. Pull-up is set correctly by ferrule advance and the gap gauge, not by how the wrench feels. For details, see ferrule installation and gauging.
Tube-End Thread Size References: NPT, BSPT, BSPP, JIC & SAE-ORB
On fittings with a threaded end, thread size stands apart from tube OD as its own spec. A 1/4" tube end can carry a 1/4" NPT, a metric, or a BSP thread. The Crestflo tube fitting thread-size chart below lists the common thread-size options for a threaded instrumentation fitting, with each governing standard and its detail page. Which thread goes on a given part is line-specific by default, and it's confirmed on the order. Not sure which thread you're working with? Use the thread identifier or the thread identification guide.
| End type | Governing standard | Detail page |
|---|---|---|
| Tube-OD (fitting) end | Sized to tube OD | tube-OD fittings |
| NPT | ASME B1.20.1 | NPT tube fittings |
| NPTF (dryseal) | ASME B1.20.3 | NPTF |
| BSPT / BSPP | ISO 7 / ISO 228 | BSPT · BSPP |
| ISO parallel | ISO 228 | ISO-parallel |
| JIC 37° flare | ISO 8434-2 / SAE J514 | JIC 37° |
| SAE-ORB | SAE J1926 | SAE-ORB |
Tube Fitting OD vs Tube Wall Thickness & Tubing Size Chart
Fitting size refers to the tube OD. It doesn't determine the tube wall thickness, which comes from pressure and alloy and drives the working-pressure rating instead. A 1/2" fitting fits every 1/2" OD tube no matter the wall, but the rated pressure of the assembly climbs as the wall gets heavier. Size the wall using the tube sizing and wall thickness guide and the tube pressure calculator, which is built on ASME B31.3. Need a broad tube size chart for the tubing itself, its OD paired with wall thickness? That's a separate reference from this fitting size chart. See the tubing size chart for tube OD × wall combinations. Values follow the applicable standard and can be adjusted to your requirement.
Tube Fitting Size Cross-Reference: Swagelok, Parker & Hy-Lok Interchange
Crestflo twin-ferrule fittings share the same tube-OD system as the major inch and metric lines and interchange dimensionally. That's backed by ASTM F1387 performance qualification, the interchange proof most competitors simply don't publish. Instead of printing a static size-equivalence table, our engineering team builds your exact interchange list against your part numbers. Request your Swagelok cross-reference, or a Parker A-Lok or Hy-Lok cross-reference, from the master interchange desk. (Swagelok® is a trademark of Swagelok Company and Parker® of Parker Hannifin; Crestflo isn't affiliated with or endorsed by them.)
Standards, Certifications & Traceability
Crestflo carries ISO 9001, 14001, and 45001 certification, along with PED approval. On top of that, it holds the standard approvals required for instrumentation tube fittings.
| Item | Standard / reference | Scope |
|---|---|---|
| Fitting performance qualification | ASTM F1387 | Dimensional interchange + performance |
| Tube material specs | ASTM A269 / A213 | Instrumentation tube |
| NPT thread | ASME B1.20.1 | Threaded ends |
| Sour-service compliance | NACE MR0175 / ISO 15156 | Qualifying alloys |
| Material test certificate | EN 10204 3.1 (3.2 on request) | Every shipment |
| Traceability | Heat / lot number on every part | Full lot linkage |
| Verification | PMI, in-house NDT | Confirms alloy + integrity |
Refer to the ASTM F1387 performance qualification and the EN 10204 3.1 material test certificate for full details. Crestflo keeps both on file, organized within its quality documentation. Need datasheets or CAD models? Just ask. We're happy to send them to customers on request.
Tube Fitting Materials by Size: 316/316L, Duplex, Inconel & Monel
Every OD on the chart is available in both stainless and corrosion-resistant alloy. No brass. Standard product ships from India; US or European melt can be arranged on request, and full material traceability comes with it.
| Alloy family | Grades | Grade page |
|---|---|---|
| Austenitic stainless | 304/304L, 316/316L, 904L | 316/316L stainless · 904L |
| Duplex / super-austenitic | Duplex 2205, Super Duplex 2507, 254 SMO, AL-6XN, Alloy 20 | duplex 2205 · super duplex 2507 |
| Nickel alloys | Inconel 625/825, Monel 400, Hastelloy C-276 | Inconel 625 · Monel 400 · Hastelloy C-276 |
| Titanium | Titanium Gr2 | titanium Gr2 |
Compositions follow the applicable ASTM/UNS specification. Check the materials index on Crestflo's site to see every grade available. This fitting comes in instrumentation form only.
Order Tube Fittings by Size: RFQ, Sample & Configurator
Crestflo supplies and manufactures tube fittings for the US market. Standard items ship from ready stock; specials get made to order, with delivery running 6–8 weeks. Once you know the OD, configure the exact part number, then request a quote or request a sample. Distributors can ask for the tube fittings line card, and OEMs should look into the private-label program. The chart lives on the page as HTML, with no PDF gate and no download form, so the sizes stay current. That's the same OD range you'll find in the Crestflo catalog, available to customers on request. Have a spec you need to talk through? Contact our engineering team at sales@crestflousa.com or +1 346 594 9005, in Houston, TX.
Why Crestflo for Tube Fitting Sizing
Crestflo is the instrumentation division of an export house that's been in business for four decades and carries Government-of-India recognition, with a proven track record delivering into the Middle East. That history stands behind every fitting: imperial and metric sizes, OD up to 2" (50 mm), and ASTM F1387 drop-in proof. Lead times run 6–8 weeks, well under the 20-plus weeks typical of the major suppliers. Small MOQs and private-label support are available too. Machining is done in-house across CNC, VMC, and EDM. Heat-number traceability comes standard, backed by EN 10204 3.1 MTC. Origin is Indian, though US or European melt can be arranged on request, with full material traceability throughout. We Engineer Confidence.
Frequently Asked Questions
Are tube fittings measured by OD or ID?
By tube OD, that's the outside diameter of the tube the fitting grips. Not the inside diameter, and not the end thread. Grab a caliper, measure the tube's outside diameter, and match the fitting to that number.
What tube sizes do Crestflo fittings come in?
Sizes span 1/16" to 2" (50.8 mm) OD on the fractional-inch side, and 2 mm to 50 mm on the metric side. Single or double ferrule, in stainless steel or high-nickel alloys. You'll find the full breakdown in the imperial and metric tables above.
Do you offer both imperial and metric tube fittings?
Yes. Every fitting comes in both measurement systems. Stick to one system per tubing run, since imperial and metric fittings don't interchange.
What is 1/4 inch in metric?
A quarter inch works out to 6.35 mm exactly, since you multiply by 25.4. The closest metric fitting size is 6 mm, but don't be fooled: a 6 mm fitting won't seal on 1/4" tube, and the reverse holds too. They're separate systems, plain and simple.
What thread pairs with a 1/4 inch compression tube fitting?
The 1/4" describes the tube's outer diameter, and that's separate from the end thread. Most threaded ends run 1/4" NPT, but you'll also see NPTF, BSPT, BSPP, ISO parallel, JIC 37° and SAE-ORB. Whatever thread a given part actually has gets confirmed on the order.
Is 1/4 NPT the same as 1/4-20?
No. 1/4 NPT is a tapered pipe thread built to ASME B1.20.1. 1/4-20, by contrast, is a straight machine-screw thread. Two separate thread systems entirely, and they don't interchange. For the full breakdown, see the thread identification guide.
How do I identify an AN fitting size?
AN and automotive fittings, covered under SAE J514 dash sizes, belong to a different system entirely and fall outside this chart. This reference deals only with instrumentation tube fittings sized by tube OD. If you're working with AN or hose sizing, look elsewhere.
What is the largest tube fitting Crestflo makes?
OD tops out at 2" (50 mm). At the small end, the fractional series bottoms out at 1/16" (roughly the 2 mm class), while the metric series goes down to 2 mm.
Do the fitting sizes change by alloy?
No. OD sizes don't shift with alloy choice. 316/316L, 904L, duplex, and the high-nickel grades all draw from the same size range. Material changes the pressure rating and the price. It doesn't touch which sizes are on offer.
Can I get the chart as a PDF?
The full tube fitting size chart lives right on the page as HTML. No PDF gate, no download form, so the sizes stay current and easy for machines to read. If you came looking for a tube fitting size chart PDF, the same OD range appears in the Crestflo catalog too, available to customers on request. We don't publish per-product datasheet PDFs.
Which tube wall thickness do I need?
Wall thickness depends on pressure and alloy, not the fitting OD. Size it using the tube sizing and wall thickness guide alongside the tube pressure calculator. Values follow ASME B31.3 and can be adjusted to fit your requirement. Crestflo built both tools with that in mind.
Do your tube fitting sizes match Swagelok or Parker?
Yes, dimensionally. Crestflo fittings share the same tube-OD system as Swagelok and the other major brands, so they interchange directly, and ASTM F1387 backs that up. Need the exact part numbers? Request a cross-reference from our engineering team.
Related Pages
- All instrumentation tube fittings
- Imperial / fractional tube fittings · metric tube fittings · metric vs imperial
- Tubing size chart · tube sizing and wall thickness
- 1/4 inch tube fittings · 1/2 inch tube fittings · 6mm tube fittings
- Part-number configurator · thread identification guide
- ASTM F1387 interchange qualification · Swagelok cross-reference