5/8" Instrumentation Tube Fittings: Stainless Steel & High-Alloy (Two-Ferrule, Drop-In)
A 5/8" tube fitting is a mechanical-grip compression fitting that seals and holds tubing with a 5/8-inch (0.625") outside diameter, driving one or two ferrules onto the tube as the nut is tightened to form a leak-tight, gas-tight joint. Crestflo manufactures the 5/8" size in 316/316L stainless and corrosion-resistant alloy, single or two-ferrule, engineered as ASTM F1387-qualified drop-in replacements for the major instrumentation fitting brands.
5/8" Tube Fitting Designations: 0.625" OD, ⅝", Twin-Ferrule & Dash-10
Buyers and specifiers also call this size a 5/8" OD tube fitting, a 5/8" OD compression fitting, a 0.625" tube fitting, a ⅝" fitting, or a 5/8 compression fitting (instrumentation). The mechanism is described as a twin-ferrule, two-ferrule or double-ferrule fitting, and a single-ferrule 5/8 fitting is offered for the same tube OD. In AN/dash hose sizing, 5/8" outside diameter corresponds to Dash-10 (−10), though that is a hose convention rather than an instrumentation tube-fitting call-out. The nearest metric neighbor is 16 mm, a distinct size (15.88 mm versus 16.00 mm) that must be ordered explicitly from the metric tube-fitting range.
Scope: 5/8" here means a 0.625" outside-diameter instrumentation compression tube fitting in stainless steel or corrosion-resistant alloy, for gauge, analyzer, hydraulic and process-tubing runs. It is not a plumbing or copper compression fitting, a garden-hose or barbed connector, or a brass automotive fitting.
How a 5/8" Two-Ferrule Compression Fitting Works: Nut, Ferrules & Tube Grip
The joint is made without flaring, soldering or welding. The 0.625" tube is inserted to the fitting shoulder, and as the nut advances it drives the ferrule set forward. In a two-ferrule (double-ferrule) design, the back ferrule hinges to grip the tube while the front ferrule forms the seal against the fitting body and tube surface; a single-ferrule design combines grip and seal in one component. Both single and double-ferrule 5/8" fittings are available, with hardened or non-hardened ferrules to requirement.
Individual components, nut-and-ferrule sets, spare ferrules and single-ferrule bodies, are covered on their own pages:
- Nut and ferrule sets
- Tube fitting ferrules, including hardened vs non-hardened ferrule selection
- Single-ferrule tube fittings and the single vs double ferrule comparison
5/8" Tube Fitting Dimensions: 0.625" OD, 15.88 mm & Where It Sits in the Imperial Series
The 5/8" fitting is sized for a nominal 0.625-inch (15.88 mm) tube outside diameter and sits in the mid-range of the imperial series, between 1/2" and 3/4". Compression tube fittings are offered up to 2" (50 mm) OD, so 5/8" is a mainstream size across the range.
| Attribute | Value |
|---|---|
| Nominal tube OD (fraction) | 5/8" |
| Decimal OD | 0.625" |
| Metric equivalent OD | 15.88 mm |
| Nearest metric size | 16 mm (distinct, order separately) |
| Ferrule design | Single or double (two-ferrule) |
| Ferrule condition | Hardened or non-hardened |
| Position in imperial series | Between 1/2" and 3/4" (series 1/8"–1") |
| AN/dash equivalent (hose sizing) | Dash-10 (−10) |
OD and wall values follow standard published tube dimensions; for the full imperial and metric series see the tube OD and wall size chart. Adjacent sizes: 1/2" tube fittings and 3/4" tube fittings.
5/8" Tube Fitting Configurations: Union, Tee, Elbow, Reducing Union & Connectors
The 5/8" size is available across the full configuration set, tube-to-tube and reducing (for example 5/8 × 1/2 or 5/8 × 1/4). Each configuration is detailed on its own page.
| Configuration | Description | Page |
|---|---|---|
| Union | Straight 5/8 tube × 5/8 tube joint | Union |
| Reducing union | 5/8 to a smaller tube OD (e.g. 5/8 × 1/2, 5/8 × 1/4) | Reducer |
| Tee | Three-way branch, union or run | Tee |
| Cross | Four-way junction | Cross |
| Elbow | 90° union, male or female | Elbow |
| Male connector | 5/8 tube to male thread | Male connector |
| Female connector | 5/8 tube to female thread | Female connector |
| Port connector | Tube-fitting-end port adapter | Port connector |
| Bulkhead union | Panel-mounting through-wall joint | Bulkhead union |
| Cap & plug | Line termination | Cap / Plug |
| Adapter | Thread-to-thread or tube-to-thread transition | Adapter |
| Weld connector | Socket, butt or orbital weld end | Weld connector |
5/8" End & Thread Connections: NPT, BSPT/BSPP, JIC 37°, SAE-ORB & Weld Ends
A 5/8" fitting connects tube-to-tube or to a threaded or welded end. Note that "5/8" describes the tube OD, not a pipe thread, there is no 5/8 pipe thread; the threaded end is sized and specified separately.
| End type | Standard | Page |
|---|---|---|
| NPT / NPTF taper thread | ASME B1.20.1 | NPT / NPTF |
| BSPT taper thread | ISO 7 | BSPT |
| BSPP / ISO parallel | ISO 228 | BSPP / ISO parallel |
| JIC 37° flare | SAE J514 / ISO 8434-2 | JIC 37° |
| SAE-ORB O-ring boss | SAE J1926 | SAE-ORB |
| Socket / butt weld | Weld-prep ends | Socket weld / Butt weld |
| Orbital weld | High-purity autogenous weld end | Orbital weld fitting |
Thread dimensions follow the applicable standard and are customizable to requirement.
5/8" Tube Fitting Materials: 316/316L Stainless, Duplex, Inconel, Monel, Hastelloy & Titanium
The core specification most instrumentation runs call out, a 5/8 inch stainless steel compression fitting, also written as a 5/8 stainless steel tube fitting or 5/8 od stainless tube fitting, is built in 316/316L. Above it, the 5/8" size is manufactured in duplex/super-austenitic and high-nickel alloys, and titanium, the corrosion-resistant metallurgy that instrumentation service demands. On this US site, 5/8" fittings are offered in stainless and alloy only, not brass. NACE MR0175 / ISO 15156 compliant material is available for sour service.
| Family | Grades (UNS) | NACE MR0175 suitable | Grade page |
|---|---|---|---|
| Austenitic stainless | 304/304L (S30400/S30403), 316/316L (S31600/S31603), 904L (N08904) | Yes (grade-dependent) | 316/316L |
| Duplex / super-austenitic | Duplex 2205 (S32205), Super Duplex 2507 (S32750), 254 SMO (S31254), AL-6XN (N08367), Alloy 20 (N08020) | Yes | Duplex 2205 |
| Nickel alloys | Inconel 625 (N06625), Inconel 825 / Incoloy 825 (N08825), Monel 400 (N04400), Hastelloy C-276 (N10276) | Yes | Hastelloy C-276 |
| Titanium | Titanium Gr2 (R50400) | Application-specific | Titanium Gr2 |
UNS designations are standard published values; compositions and grades are per the applicable ASTM specification and customizable to requirement. Browse all 316/316L and alloy material options.
Working Pressure & Temperature: Rated by Tube Wall, Alloy & Temper
The working pressure of a 5/8" tube joint is a function of the tube outside diameter, wall thickness, alloy and temper, not the fitting body alone. Ratings are established from standard tube-pressure tables and allowable-stress values (per ASME B31.3), which vary with material and temperature; values are per the applicable standard and customizable to requirement. Size your 5/8" run with the tube pressure and wall-thickness calculator and review pressure-temperature derating for elevated-temperature service.
Standards, Certifications & Traceability: ASTM F1387, NACE, ISO & MTC 3.1
Crestflo 5/8" tube fittings are manufactured and qualified to the standards applicable to instrumentation compression fittings.
| Item | Standard / basis |
|---|---|
| Fitting performance qualification | ASTM F1387 (interchange/drop-in basis) |
| Sour-service materials | NACE MR0175 / ISO 15156 |
| Bar stock | ASTM A276 / A479 |
| Instrumentation tube | ASTM A269 |
| NPT threads | ASME B1.20.1 |
| Material traceability | EN 10204 MTC 3.1 standard / 3.2 on request; heat/lot number on every part |
| Company quality system | ISO 9001 / 14001 / 45001 & PED certified |
Every part carries a heat/lot number for full traceability, and each order ships with EN 10204 MTC 3.1 (3.2 on request). Testing covers hydraulic proof, burst and impulse, pneumatic, pull-out, vacuum, thermal cycling, flexure/rotary-flex and vibration, with PMI and in-house NDT; destructive testing is performed at ISO/IEC 17025-accredited labs and third-party inspection is available on request. Certificates are held in the quality section, and full material traceability documentation accompanies each shipment.
Order 5/8" Tube Fittings: Quote, Sample & Cross-Reference
Crestflo is an RFQ manufacturer, not a retail catalog: pricing and availability are confirmed on quote. Ready stock for standard items · made-to-order for specials · 6–8 week delivery.
- Request a quote for your 5/8" configuration, material and thread combination.
- Request a sample to validate fit and finish.
- Request your Swagelok® or Parker® cross-reference from the cross-reference desk, send the part you run today and our engineering team returns the interchange.
- Datasheets and CAD models are available to customers on request.
Swagelok®, Parker®, Hoke®, Hy-Lok® and Fitok® are trademarks of their respective owners (for example, Swagelok® is a trademark of Swagelok Company). All brand names are used for identification and interchange-reference purposes only and do not imply affiliation with or endorsement by those companies.
US inquiries: sales@crestflousa.com · +1 346 594 9005 · Houston, TX. Ordering-code guidance and full part-number breakdowns are provided by the engineering team on request.
Why Crestflo for 5/8" Instrumentation Tube Fittings
As a 5/8" tube fitting supplier and manufacturer serving the US, Crestflo is the instrumentation division of a four-decade-old, Government-of-India-recognized export house with an established Middle-East delivery record, engineering depth behind a focused instrumentation brand.
- F1387 drop-in interchange, dimensionally engineered as an equivalent to Swagelok®, Parker®, Hoke®, Hy-Lok® and Fitok®, backed by ASTM F1387 performance qualification.
- 6–8 week delivery versus the 20+ weeks typical of the majors.
- Cost-competitive after US duties, with small MOQ and private-label options.
- Imperial and metric across the full fitting range, single or double ferrule, hardened or non-hardened.
- Full traceability, heat/lot number on every part with MTC 3.1/3.2.
- Indian origin; US / European melt available on request, with full material traceability.
Explore all instrumentation tube fittings, Crestflo lead time, private-label and US origin & compliance.
5/8" Tube Fitting FAQ
What is a 5/8" tube fitting?
A 5/8" tube fitting is a compression fitting that grips and seals onto tubing with a 5/8-inch (0.625") outside diameter using a nut and one or two ferrules. On this site it refers to instrumentation fittings in stainless steel or corrosion-resistant alloy, not plumbing or copper compression fittings.
How do you install a 5/8" tube fitting?
Standard published practice: cut and deburr the 0.625" tube square, insert it fully to the fitting shoulder, and finger-tighten the nut. Mark the nut, then pull up the wrench about 1‑1/4 turns to set the ferrules, and verify the pull-up with a gap-inspection gauge before pressurizing. The exact procedure is customizable to the configuration, ferrule type and service requirement.
Is there a 5/8 pipe thread?
No. "5/8" refers to the tube outside diameter, not a pipe thread. A 5/8" fitting connects to threaded ends through separately sized NPT, BSPT/BSPP, JIC 37° or SAE-ORB threads, so the thread size is specified independently of the tube OD.
What is the AN or dash equivalent of 5/8"?
In AN/dash sizing a 5/8" outside diameter corresponds to Dash-10 (−10), a convention common in hose applications. Crestflo's 5/8" products are instrumentation tube fittings rather than hose ends, so the Dash-10 label is a cross-reference note, not the ordering size.
What materials are 5/8" fittings available in?
Stainless 304/304L, 316/316L and 904L; duplex 2205, super duplex 2507, 254 SMO, AL-6XN and Alloy 20; Inconel 625, Inconel/Incoloy 825, Monel 400 and Hastelloy C-276; and titanium Gr2. NACE MR0175 / ISO 15156 compliant grades are available for sour service.
Are 5/8" Crestflo fittings a drop-in for Swagelok or Parker?
They are engineered for dimensional interchange and qualified per ASTM F1387, so they function as an interchange or equivalent for the major two-ferrule brands. Send the part you run today for a confirmed cross-reference before ordering.
Are single and double (two-ferrule) 5/8" fittings available?
Yes. Both single-ferrule and double-ferrule (two-ferrule) 5/8" designs are offered, with hardened or non-hardened ferrules selected to the service requirement.
Are 5/8" fittings NACE-compliant for sour service?
Yes. The 5/8" size is available in NACE MR0175 / ISO 15156 compliant alloys such as 316/316L, duplex, super duplex and nickel alloys for H2S and sour-service applications.
What certifications and documentation come with them?
Crestflo is ISO 9001 / 14001 / 45001 and PED certified. Each 5/8" order ships with EN 10204 MTC 3.1 material certification (3.2 on request) and a heat/lot number on every part; PMI and test records are available on request.
What is the lead time and minimum order?
Ready stock for standard items, made-to-order for specials, with 6–8 week delivery. Small minimum order quantities and private-label programs are available.
Where are 5/8" fittings made and are they TAA-eligible?
Standard product is Indian origin, with US / European melt available on request and full material traceability. TAA/domestic-melt requirements are handled as a capability, see the US origin and compliance page for details.
What is the metric equivalent of 5/8"?
5/8" equals 15.88 mm, which is close to but distinct from 16 mm. Because 15.88 mm and 16.00 mm are different tube outside diameters, order the metric size explicitly from the metric tube-fitting range rather than substituting one for the other.