How to Install & Gauge Instrumentation Tube Fitting Ferrules (Step-by-Step)
Ferrule installation and gauging is the process of assembling, tightening, and inspecting an instrumentation tube fitting so the ferrule (or ferrules) swages onto the tube and grips and seals on the first make-up. Start by cutting the tube square and deburring it, then bottom it out fully in the fitting body and tighten the nut finger-tight. From there, pull up 1-1/4 turns (3/4 turn for 3/16" (5 mm) tube and smaller), and check the make-up with a gap inspection gauge. Once that's done, the ferrules bite into the tube and seal on its outside diameter.
In this context, ferrule means a fluid-system compression ferrule: the metal sleeve that grips and seals tubing inside a tube fitting. It's not an electrical wire-end ferrule, and it isn't a plumbing compression olive either.
Ferrule Installation Is Also Called Tube Fitting Make-Up, Pull-Up or Assembly
Ask ten technicians what to call this operation and you'll get ten answers. Drawings and installation SOPs might label it tube fitting installation, tube fitting assembly, tube fitting make-up, or tube fitting pull-up. On compression (bite-type) hardware, it's compression fitting installation, or just "tightening a compression fitting." The check that follows goes by just as many names: gap inspection, gap-gauge check, gaging, gauging, a no-go gauge check. Call it what you like. The mechanics underneath don't change: bottom the fitting, snug it finger-tight, count your turns, gauge the result. That holds true whether you're working with two-ferrule (double-ferrule) or single-ferrule designs, and it holds across 316/316L, duplex, 6-Moly, nickel-alloy and titanium tube.
What a Ferrule Does: Nut, Body, Back Ferrule (Grip) & Front Ferrule (Seal)
A tube fitting has four working parts: the body, which is the port the tube bottoms into; the nut, the piece you actually turn; and, on a two-ferrule design, a back ferrule and a front ferrule that ride on the tube. As the nut advances, the back ferrule collets radially onto the tube's outside diameter and delivers mechanical grip, resistance to pull-out and vibration. The front ferrule gets driven forward at the same time, forming the primary seal against the body's tapered bore. A single-ferrule design skips that division of labor; one component handles both grip and seal.
Not sure what a ferrule actually is? See what a ferrule is for the definition. If you're weighing designs, single vs double ferrule, which to use and hardened vs non-hardened ferrules walk through the differences.
Before You Start: Tube, Tools & Materials for Tube Fitting Assembly
Correct make-up depends on the tube every bit as much as the fitting. The tube has to be the right outside diameter and wall thickness for the fitting series (choosing tube OD and wall thickness), and as a general instrumentation rule, it should be softer (fully annealed) than the fitting body so the back ferrule can bite into it. This applies across stainless (304/304L, 316/316L, 904L), duplex and super-duplex, 254 SMO and AL-6XN, nickel alloys, and titanium Grade 2 instrumentation tube. Harder alloy tube, though, typically calls for a hardened ferrule if you want a reliable grip.
Cut the tube square, call it good within roughly 0.010" / 0.25 mm of true, then deburr both the inside and outside diameters. Wipe the tube clean before you move on to assembly.
Tools & Consumables Checklist for Ferrule Installation
| Item | Purpose | Notes |
|---|---|---|
| Tube cutter | Cut tube square to length | Rotary or precision cutter; avoid ovalising the tube |
| Deburring tool | Remove ID/OD burrs | Burrs prevent full seating and can score the ferrule |
| Nut wrench | Drive the nut | Sized to the fitting nut |
| Backup wrench | Hold the body steady | Prevents the body rotating during pull-up |
| Gap inspection gauge | Verify pull-up (no-go check) | Sized to the fitting; for initial installation |
| Pre-swaging tool / hydraulic swaging unit | Preset ferrules (optional) | Useful for large OD, heavy wall, limited access |
| Lint-free wipe | Clean the tube | No thread sealant on the tube or ferrules |
Step-by-Step: Double-Ferrule Tube Fitting Make-Up & Pull-Up
The compression fitting installation steps below follow the standard published industry method for two-ferrule instrumentation compression fittings. Values reflect the applicable standard make-up method, and they can be adjusted to match your fitting series. Ask us for the exact turns on a specific Crestflo part.
- Bottom the tube. Push it all the way into the fitting body until it hits the internal shoulder. A tube that hasn't bottomed out is, by far, the most common reason a joint refuses to seal.
- Finger-tighten the nut. Rotate the nut hand-tight (finger-tight) onto the body.
- Check ferrule orientation. On a two-ferrule set, the back ferrule's taper points toward the nut, while the front ferrule's taper points toward the body. Get this backward and the ferrules won't seal. Confirm the taper direction before you pull up.
- Mark the nut. Scribe a witness mark on the nut at a reference position, say 6 o'clock, so you can count turns accurately.
- Pull up by counted turns. Hold the body steady with the backup wrench and pull the nut up 1-1/4 turns past finger-tight for tube 1/4" (6 mm) and larger. For 3/16" (5 mm) and smaller, it's 3/4 turn past finger-tight. Check the pull-up table below for details. That witness mark is what makes the count unambiguous.
- Made up by turns, not torque. Instrumentation tube fittings go together by counted turns of the nut, not a torque value. Turns produce a repeatable ferrule advance no matter how much friction is in the threads, which keeps the grip and seal consistent from one joint to the next.
Pull-Up by Tube OD: The 1-1/4 Turn Rule (& 3/4 Turn for 3/16" and Smaller)
| Tube OD (imperial) | Tube OD (metric) | Pull-up past finger-tight (standard method) |
|---|---|---|
| 1/16" | ~1.6 mm | 3/4 turn |
| 1/8" | ~3 mm | 3/4 turn |
| 3/16" | ~5 mm | 3/4 turn |
| 1/4" | 6 mm | 1-1/4 turns |
| 3/8" | 8–10 mm | 1-1/4 turns |
| 1/2" | 12 mm | 1-1/4 turns |
| 5/8" | 16 mm | 1-1/4 turns |
| 3/4" | 18–20 mm | 1-1/4 turns |
| 1" to 2" | 25–50 mm | 1-1/4 turns |
Values here follow the standard published make-up method for two-ferrule fittings across the industry, though they can be adjusted to suit the fitting series. Need the exact turns certified for a specific Crestflo part number? Request the ordering-code and make-up reference from our engineering team.
Single-Ferrule Installation: How Make-Up Differs
On a single-ferrule tube fitting, one ferrule does both jobs: gripping and sealing. Prep works the same way as always, bottom the tube, finger-tighten, mark the nut. From there, though, you follow the pull-up spec for that particular single-ferrule series instead of the two-ferrule turn counts described above. With only one moving element, single-ferrule designs get chosen for having fewer parts and a simpler assembly process. The trade-offs against two-ferrule and ferrule-less designs are covered in single vs double vs ferrule-less, and Crestflo lays them out in more detail there.
Gauging & Inspection: Using a Gap Inspection Gauge (No-Go Check)
A gap inspection gauge checks whether a newly installed fitting has been pulled up far enough. Once you've pulled it up, slide the gauge into the gap between the nut and the body. It's a no-go check. If the gauge won't fit into the gap, the fitting has been pulled up enough and passes. Enter the gap, though, and the fitting isn't pulled up enough: tighten it further and check again. Keep in mind, the gauge only confirms initial installation. It doesn't verify remakes; those are set by returning the nut to its marked position.
Gap-Gauge Decision Table
| Observation | Meaning | Action |
|---|---|---|
| Gauge will not enter the gap | Sufficiently pulled up | Accept the joint |
| Gauge enters the gap | Insufficient pull-up | Tighten further, then re-gauge |
| Fitting is a remake | Gauge not applicable | Follow the remake method (return to marked position) |
Gap gauges are matched to the fitting size. To get the right gauge for your tube sizes, reach out to Crestflo's engineering team and request the gap-gauge reference for your part numbers.
Pre-Swaging (Presetting) Ferrules with a Swaging Tool
Pre-swaging, or presetting, sets the ferrules onto the tube using a swaging tool or hydraulic swaging unit before the final assembly goes into the body. It's the right call for large outside diameters, heavy-wall tube, bulkhead joints, or anywhere access is tight. High-volume production benefits too, since consistency matters more as the numbers climb. The sequence itself doesn't change: the tool advances the ferrules onto the tube, the preset gets verified, and then the tube-and-ferrule assembly goes into the fitting body and gets pulled up to complete the joint. Nothing about the seal-and-grip mechanics shifts. Presetting just moves the swaging step to a bench or tool, where you get better control and easier access.
Remakes: Disassembly, Reassembly & Reusing the Tube/Ferrule Assembly
The two-ferrule design was made with remakes in mind. Once you swage the ferrules, they stay on the tube for good, so you reuse that same tube-and-ferrule assembly instead of installing new ones. Here's how you remake a joint: slide the tube-and-ferrule assembly back into the body, then thread the nut down until you feel the ferrules re-seat. You'll notice a marked jump in resistance right at the position you marked earlier. Give it a slight extra turn to snug it up. Don't use a gap gauge on remakes; it isn't needed here. This is how two-ferrule instrumentation designs allow for repeated disassembly and reassembly. If a joint still leaks after a proper remake, see why a tube fitting leaks after install.
Common Tube Fitting Installation Mistakes & How to Avoid Them
| Symptom | Likely cause | Fix / owner page |
|---|---|---|
| Leak at the nut | Under-pull-up or damaged ferrule | Pull up to spec / remake, or see troubleshooting |
| Cracked ferrule, split nut or galled tube | Over-tightening past the counted turns | Make up by counted turns, not force, the gap gauge confirms enough pull-up, so stop there rather than over-torquing |
| Tube pulls out or slips | Tube not bottomed before make-up | Reseat the tube fully, remake |
| Joint won't seal | Reversed ferrule orientation | Reset front/back ferrule taper direction |
| Uneven seal / galling | Out-of-square or burred tube cut | Re-cut square, deburr ID/OD |
| Inconsistent grip on alloy tube | Non-hardened ferrule on hard tube | Specify a hardened ferrule for the alloy |
| Fit or seal problems after mixing hardware | Intermixing fitting brands | See risks of mixing fitting brands |
Standards & Proof: ASTM F1387, Testing & Traceability
Crestflo compression tube fittings meet ASTM F1387, the performance standard for mechanically attached fittings. It's the same standard that sets dimensional interchange and governs how the fittings make up and gauge. Qualification rests on a full battery of tests: pull-out, hydraulic proof, burst and impulse, vibration and flexure fatigue, and thermal cycling. Each part carries a heat-number mark, so full traceability comes standard. EN 10204 3.1 material test certificates ship with every order, and 3.2 is available on request. Crestflo also holds ISO 9001, 14001 and 45001 certification, along with PED.
For a closer look at ASTM F1387 performance qualification, Crestflo has a dedicated page worth checking. There's also a separate resource on material test certificates and heat-number traceability, handy if you need to trace parts back to their heat number.
Crestflo Ferrules & Tube Fittings: Options and How to Order
Crestflo builds instrumentation tube fittings, and the catalog goes further: replacement ferrules, single and double and nut-and-ferrule sets round it out. All of it comes in imperial and metric sizes.
| Attribute | Options |
|---|---|
| Ferrule count | Single-ferrule or two-ferrule (double-ferrule) |
| Ferrule hardening | Hardened or non-hardened, to requirement |
| Materials | 316/316L, 904L, Duplex 2205, Super Duplex 2507, 254 SMO, AL-6XN, Alloy 20, Inconel, Incoloy, Monel, Hastelloy, Titanium Gr2 |
| Size range | Up to 2" (50 mm) OD; imperial and metric |
| Traceability | Heat-number marked; EN 10204 3.1 MTC standard, 3.2 on request |
| Standard | Qualified to ASTM F1387; NACE MR0175 / ISO 15156 compliant materials |
Availability: Standard items ship from ready stock. Specials are made to order, and those typically take 6–8 weeks to deliver. Origin: Material is of Indian origin. US or European melt can be arranged on request, and full material traceability comes with it either way.
To move from guide to parts, request a quote or free samples or build a part number. To replace an existing brand, request your cross-reference from our engineering team.
Why Crestflo for Instrumentation Tube Fittings & Ferrules
Crestflo is the instrumentation division of a four-decade-old export house recognized by the Government of India, with a proven delivery record across the Middle East. Behind this focused, US-serving instrumentation brand sits real engineering and quality depth. Crestflo tube fittings and ferrules are qualified to ASTM F1387. They come with hardened or non-hardened ferrules depending on what the job calls for, in single and double-ferrule designs up to 2" OD, across stainless, high-nickel, and titanium alloys. Every part ships with heat-number traceability and an MTC. US buyers get engineered drop-in replacement, small MOQs, private-label options, and a 6–8 week lead time. We Engineer Confidence.
Talk to us: sales@crestflousa.com · +1 346 594 9005 (Houston, TX).
Frequently Asked Questions: Ferrule Installation & Gauging
How do you connect tubing to a tube fitting?
Seat the tube fully into the fitting body, then snug the nut down finger-tight. Mark the nut before going further. From there, turn it 1-1/4 turns past finger-tight (just 3/4 turn if the tube is 3/16" or smaller). As you tighten, the ferrules swage onto the tube's outside diameter, gripping it and forming the seal.
How many turns do I tighten a tube fitting?
Industry standard calls for 1-1/4 turns past finger-tight on 1/4" / 6 mm tube and larger, and just 3/4 turn on 3/16" / 5 mm and smaller. Always follow the make-up specified for your exact fitting series. Crestflo's figures track the applicable standard and can be adjusted to your requirements.
Should I torque tube fittings to a value?
No. Instrumentation tube fittings get made up by counted turns of the nut, not to a torque figure. Turns don't care about thread friction the way torque does. Count them out, and you get the same ferrule advance every time, joint after joint, which is what gives you a consistent grip and a reliable seal.
What is a gap inspection gauge and how do I use it?
This is a no-go gauge, set into the gap between the nut and the body once pull-up is complete. If it won't fit into that gap, the fitting has been pulled up enough and passes. Enter the gap, though, and the fitting is under-pulled-up. Keep in mind: the gauge applies only to initial installation, not remakes.
Which way does the ferrule face?
On a two-ferrule set, the back ferrule's taper points toward the nut, while the front ferrule's taper points toward the body. Get that backward and the joint won't seal. Check the orientation before you pull up.
Can I reuse a ferrule or remake the fitting?
Swaging locks the ferrules onto the tube for good. That means you reuse the same tube-and-ferrule assembly each time, not a fresh set of ferrules. When you put it back together, bring the nut back to the mark you made earlier and give it just a touch more rotation to snug it down. Two-ferrule designs are built for this kind of repeated remake.
What is pre-swaging?
Pre-swaging, or presetting, seats the ferrules onto the tube using a swaging tool or hydraulic unit before final assembly happens. It's the right call for large sizes, heavy-wall tube, and joints with limited access, and it helps keep production consistent. Once that's done, the tube-and-ferrule assembly gets completed into the body.
How do I install a Swagelok® tube fitting?
Stick with the same make-up and gauging method: bottom it, turn finger-tight, count the turns, then check with a gap gauge. Crestflo fittings are dimensionally interchangeable and qualified to ASTM F1387. Swagelok® is a trademark of Swagelok Company, and Crestflo isn't affiliated with or endorsed by it. Need to match parts? Request your cross-reference.
How do I connect pipe to tube?
Use a fitting with the right threaded (pipe) end and the correct tube-fitting end. Start by identifying the thread with Crestflo's thread identification guide, then make up the tube end using the method described above.
Do hardened ferrules install differently?
The make-up method is identical. Hardened ferrules grip harder alloy tube better, which is why they're specified for materials like duplex and nickel alloys. Crestflo offers hardened and non-hardened ferrules to requirement.
Which alloys can I install this way?
The same process applies to 316/316L, 904L, Duplex 2205 and Super Duplex 2507, 254 SMO, AL-6XN, Alloy 20, Inconel, Incoloy, Monel, Hastelloy, and Titanium Grade 2 instrumentation tube. Where the tube is hard, specify a hardened ferrule.
Does metric or imperial change the method?
No, the bottom, finger-tight, counted-turn, and gauge steps stay the same across sizes. Only the turn count and gauge specific to that size change. For help matching sizes, see metric vs imperial tube fittings from Crestflo.