How to find the right Compression Fittings AI guide
Written by an AI model from its trained knowledge.
What the AI looks for in Compression Fittings
- Tube outside diameter
- Match the fitting to the tube OD exactly. Fractional-inch and metric sizes are not interchangeable, even where they look close (3/8 in vs 10 mm, 1/4 in vs 6 mm). The ferrule only seals on the OD it was machined for. A near-miss size leaks or blows off under pressure.
- Fitting material vs tube material
- Use stainless fittings on stainless tube, and brass on copper, aluminum or plastic tube. The tube should be softer than the ferrule. Dissimilar hardness or metals cause poor bite, galling or galvanic corrosion.
- Ferrule design
- Two-ferrule instrumentation fittings suit high pressure, vibration or gas service. Single-ferrule (olive or sleeve) brass fittings suit low-pressure water and air. Two-ferrule designs grip and seal separately and resist vibration and gas leaks far better.
- Brand intermix
- Keep the body, nut and ferrules from the same manufacturer and series. Thread forms, cone angles and ferrule geometry differ between makers, and intermixing voids pressure ratings.
- Tube wall and soft-tube support
- Check the maker's minimum and maximum wall table. Add a tube insert for plastic or thin-wall soft tubing. Thin or soft walls collapse under the ferrule and leak or pull out.
- End connection type
- Confirm the other end is tube, NPT, BSPP/BSPT or SAE/ISO port, and match it exactly. Many fittings have one compression end and one threaded end, and the thread standards do not cross-seal.
Brands that matter
- Swagelok: Reference two-ferrule instrumentation fitting; the most widely documented sizes and installation gauges.
- Parker: A-Lok two-ferrule and CPI single-ferrule instrumentation lines, with broad distribution.
- Hy-Lok: Two-ferrule instrumentation fittings in common industrial use.
- Ham-Let: Instrumentation compression fittings and valves.
- Hoke: Gyrolok compression fitting line.
- Dk-Lok: Two-ferrule instrumentation fittings.
- Anderson Metals: Brass low-pressure compression fittings for water, air and fuel lines.
What to avoid
- Unbranded "compatible" fittings mixed with name-brand ferrules or nuts in pressure or gas service
- Using a plumbing olive-type fitting in high-pressure, gas or vibrating instrument lines
- Using metric fittings on inch tube or the reverse
- Pipe thread sealant or tape on the compression threads themselves
- Brass fittings on stainless tube
Questions
Is a compression fitting the same as a flare or push-to-connect fitting?
No. Compression fittings seal with a ferrule swaged onto the tube by the nut. Flare and push-to-connect use different seals, and their parts do not interchange.
Can I remake a compression joint?
Usually yes. The ferrule stays on the tube, and you retighten to the original position plus a slight snug per the maker's instructions, but the ferrule cannot be moved to a new tube.
Compression Elbow Fittings
Compression elbows follow the parent rules: match tube OD and material exactly, keep the body, nuts and ferrules from one maker, and choose the end types needed (tube-to-tube union elbow, or male or female pipe-thread elbow).