Stainless Steel Tube Fittings

Stainless steel tube fittings are twin-ferrule compression connectors that seal plain-cut SS tube gas-tight and can be broken and remade. Vikay supplies SS 316 male and female connectors, unions, elbows, tees, crosses, reducers and bulkheads in fractional (1/8-1 in) and metric (3-25 mm) tube sizes with NPT, ISO and SAE threads.

The twin-ferrule tube fitting is the standard connection on instrument impulse, sample and analyser lines. A back ferrule drives the front ferrule into the tube and the body taper at once, so the joint both grips and seals, and it can be remade many times without a new fitting.

This is Vikay's largest stainless family, with more than 1,600 part numbers. Patterns include male connectors to NPT, ISO tapered, ISO parallel, O-seal and SAE-MS straight threads, bored-through male connectors for probe and thermocouple work, female connectors, union connectors, union elbows and tees, run and branch tees, crosses, reducing unions and reducers, port connectors, bulkhead unions, elbows and tees, caps and plugs.

Bodies are machined from SS 316 bar to ASTM A276 / A479, with 316L on request; ferrules are hardened relative to the body so the tube is gripped rather than the body galled. Threads are cut to ASME B1.20.1 (NPT), ISO 7/1, ISO 228 or SAE J514 UNF. Dimensions follow the common industry twin-ferrule pattern and are interchangeable size for size; brand names, where used, identify fitment only. Send tube OD, wall, thread form and pattern for a quote.

Frequently Asked Questions

How do I tighten a twin-ferrule tube fitting correctly?

Insert the tube fully so it seats in the body shoulder, tighten the nut finger-tight, mark the nut at the six o'clock position and then turn it one and a quarter turns to the nine o'clock position for sizes 1/4 inch and above. Smaller sizes take three quarters of a turn. Remakes need only finger-tight plus a light snug-up.

Can I mix ferrules and nuts between brands?

No. Ferrule geometry, hardness and taper differ between makers even where the parts appear identical, and a mixed joint may pass a leak test and then fail under vibration or thermal cycling. Use body, nut, front and back ferrule from one supplier within a joint.

What tube should be used with SS 316 twin-ferrule fittings?

Fully annealed, high-quality seamless SS 316 or 316L instrument tube to ASTM A269 or A213, with an even wall and no hard drawn condition. Tube harder than the ferrule will not allow the ferrule to bite, which is the commonest cause of a joint that will not stop weeping.

What does a bored-through connector do?

A bored-through male connector has no internal shoulder, so tube, probe or thermocouple sheath can pass right through the fitting and be clamped at any depth. It is used for inserting sensors into a process line at an adjustable immersion.

Do you supply fittings in 316L or 304?

SS 316 is standard production. 316L is available where a low-carbon grade is specified, and 304 on request for lower-corrosion duty. Note the grade on your enquiry along with any requirement for EN 10204 3.1 mill certificates, which must be reserved before machining.