Tube Fittings for Instrument, Process and High-Purity Lines

Tube fittings tie small-bore instrument tubing to valves, manifolds, transmitters and pipe ports. R-LOK supplies three families: double-ferrule compression, threaded pipe and tube, and high-purity weld fittings. Sizes run 1/16 in to 1 in (1.6 mm to 25.4 mm) in 316 and 316L stainless steel, with NPT, ISO and weld ends. CHANGSHA RUNDA HITECH CO., LTD. has supplied this range since 2006.

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Key features

Tube sizes 1/16 in to 1 in (1.6 mm to 25.4 mm).
Metric tube sizes 2 mm to 25 mm outside diameter.
316 and 316L stainless steel bodies, nuts and ferrules.
NPT threads per ASME B1.20.1; ISO 7/1 and ISO 228 on request.
Working pressure reaches 6,000 psi (413 bar) on small heavy-wall tube.
Silver-plated or lubricated threads reduce galling in repeated 316 make-up.

Specifications

Parameter	Value
Fitting families	double-ferrule compression; threaded pipe and tube; high-purity weld and VCR face seal
Tube sizes	1/16 in to 1 in (1.6 to 25.4 mm); metric 2 to 25 mm
Tube wall	0.028 in to 0.065 in (0.7 to 1.65 mm) in catalogue tables
Pipe threads	1/8 in to 1 in NPT; ISO 7/1 and ISO 228 on request
Working pressure	to 6,000 psi (413 bar) on small heavy-wall tube, falling as diameter grows
Temperature	to 450 °F (232 °C) for all-metal joints, lower with a soft seal
Configurations	unions, connectors, bulkheads, reducing adapters, 45° and 90° elbows, tees, crosses, caps, plugs
Ferrules	single-use and matched to the body series; replacements supplied separately

How the three families seal

Two ferrules inside a nut hold the tube. The front ferrule bites the tube wall and seals; the back ferrule grips the tube and takes the pull-out load. Make-up is by hand with two wrenches; no heat or sealant touches the tube end.

Threaded fittings seal on the thread or at a shoulder: NPT taper threads need a sealant; ISO 228 parallel threads need a gasket or bonded washer. Weld ends fuse the tube to a flat, square end, so no thread or elastomer touches the media.

How to specify a fitting

Start with the tube, not the fitting. The pressure rating belongs to the tube outside diameter and wall thickness; 1/16 in heavy-wall and 1 in lines differ. Lines broken for maintenance suit double-ferrule or VCR joints; welded lines suit butt-weld ends.

To quote, send tube outside diameter and wall, end configurations, body material, fluid, pressure, temperature and quantity. Match each port as NPT, ISO 7/1, ISO 228 or tube end; the four are not interchangeable, and mixed threads cause most rework.

Materials and make-up practice

Bodies, nuts and ferrules are 316 or 316L stainless steel; 316L suits high-purity and pharmaceutical duty. Ferrules run harder than the body so they bite the tube rather than galling the seat. Standard bodies are machined from bar stock, larger weld bodies from forgings.

Insert the tube fully against the shoulder, then turn the nut the specified number of flats. Ferrules are single-use: remake joints with new ferrules and a fresh tube end. For NPT, use PTFE tape or anaerobic sealant and leave the first two threads clean.

Standards referenced: NPT threads to ASME B1.20.1; ISO 7/1 taper and ISO 228 parallel threads for BSP options; ASME B31.3 pressure ratings; ASTM A276 / A479 wetted parts.

Typical duties: Instrument hook-up and impulse lines, oil and gas; Refinery analyser, sampling and dosing systems; Semiconductor and ultra-high-purity gas panels; Hydrogen, nitrogen and specialty gas skids; Pharmaceutical and biotech clean utilities; Hydraulic and pneumatic control panels and test benches.

Frequently asked questions

Do you have a minimum order quantity?

No fixed minimum. Trial quantities of standard items are accepted so you can fit and leak-test one line before a project order, and mixed orders across the three families are consolidated into one shipment with one document set.

Which documents and packing come with an order?

The packing list and commercial invoice are standard; on request we add the mill material certificate traceable to the heat number and a dimensional inspection report. Third-party inspection and special test reports are arranged on request. Fittings ship in seaworthy cartons with thread protectors.

Can you supply BSPP or BSPT threads?

Yes. NPT follows ASME B1.20.1; ISO 7/1 taper and ISO 228 parallel threads are supplied on request. The threads are not interchangeable, so mark each port with its thread standard. Taper threads seal with a sealant; parallel threads need a gasket or bonded washer.

Request a quote or technical clarification

Send us the model, size, material and quantity you need — or a photo of the existing part. We reply with a quotation, availability and the applicable documents, usually within one working day.

Email nimo@runda-hitech.com

WhatsApp +86 136 5741 6007

Tel / WhatsApp: +86 136 5741 6007 · Email: nimo@runda-hitech.com