TES-LOK brand | Two Different ODs — One Fitting | SS 304 / SS 316 / Brass | 6000 PSI | ISO 9001:2015
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A reducing union tube fitting is a compression tube fitting that connects two tubes of different outside diameters (ODs) in a single, leak-tight, re-makeable joint. Each end of the body accommodates a different tube OD — with its own nut and ferrule set sized to match — so a size transition is made directly at the fitting without additional reducers, adapters, or threaded nipples.
Tesco Steel manufactures reducing unions under the TES-LOK brand using a precision double-ferrule design on both ends. Common applications include connecting a 1/4" instrument sensing line to a 1/2" main process header, transitioning between metric and fractional tubing systems, or bridging two differently sized sections of a sample-conditioning loop. TES-LOK reducing unions are dimensionally compatible with Swagelok and Parker A-LOK equivalents for drop-in replacement.
| TES-LOK Reducing Union Tube Fitting — Technical Data | |
|---|---|
| Brand | TES-LOK (Tesco Steel & Engineering) |
| Fractional Size Range | 1/16" OD to 2" OD (both ends, any combination) |
| Metric Size Range | 2 mm OD to 50 mm OD (both ends, any combination) |
| Mixed Configurations | Metric OD × Fractional OD available on request |
| Material Grades | SS 304 (1.4301), SS 316 (1.4401), Brass, Monel 400, Inconel 600, Hastelloy C-276, Titanium Gr. 2 |
| Thread Standards | NPT, BSP, BSPT, UNF, ISO, SAE (end-connection threads where applicable) |
| Pressure Rating — SS | Up to 6000 PSI (413 bar) — governed by the smaller-bore end |
| Pressure Rating — Brass | 300 PSI / 1000 PSI / 3000 PSI (size-dependent) |
| Temperature Range | 150 °C to 400 °C |
| Standards | ASTM D1710, ASTM D3294 |
| Connection Design | Double-ferrule compression both ends (independent nut + front ferrule + back ferrule per end) |
| Surface Finish | Electropolished / Passivated / As-machined |
| Certifications | ISO 9001:2015; NABL-traceable MTRs available |
| Large End (OD) | Small End (OD) | Typical Application |
|---|---|---|
| 1/4" | 1/8" | Instrument gauge line to small-bore sensor port |
| 3/8" | 1/4" | Sample loop header to instrument tapping |
| 1/2" | 1/4" | Process header to 1/4" instrument sensing line |
| 1/2" | 3/8" | Flow transmitter impulse line transition |
| 3/4" | 1/2" | Larger process sample line to analyser connection |
| 1" | 3/4" | High-flow sampling header to sub-distribution header |
| Metric 12 mm | Fractional 3/8" | European instrument loop to US gauge connection |
| Metric 10 mm | Fractional 1/4" | Metric tubing to fractional instrument port bridging |
One fitting replaces a concentric reducer plus two equal unions — fewer leak points, less bulk, faster installation.
Independent double-ferrule compression on each end — disconnect and re-make either tube without disturbing the other side.
Mixed metric-to-fractional configurations available — bridge European and North American tubing systems in a single body.
Dimensionally interchangeable with Swagelok and Parker A-LOK reducing unions — direct drop-in replacement.
SS 316 with molybdenum for chloride and marine service; Hastelloy C-276 and Monel for aggressive process media.
Up to 6000 PSI in SS — suitable for high-pressure instrument impulse lines, hydraulic sensing, and process sampling loops.
| Method | Fittings Required | Leak Points | Re-makeable? | Best For |
|---|---|---|---|---|
| Reducing Union | 1 fitting | 2 | Yes — both ends | Clean, compact tube-to-tube OD transition |
| Equal Union + Concentric Reducer + Equal Union | 3 fittings | 4+ | Yes — complex | Only where single reducing union not available |
| Reducing Hex Nipple | 1 fitting | 2 (threaded) | With PTFE re-tape | Threaded pipe systems, not tube OD transitions |
| Male Adapter + Reducing Hex Coupling | 2+ fittings | 4+ | Partial | Tube-to-thread transitions with size change |
| Industry | Application | Typical Size Transition |
|---|---|---|
| Oil & Gas | Connecting 1/4" instrument sensing lines to 1/2" process sample headers; wellhead analyzer loops | 1/2" × 1/4", 3/8" × 1/4" |
| Chemical & Petrochemical | Analyzer sample conditioning — size transitions between conditioning module ports | 3/8" × 1/4", 1/2" × 3/8" |
| Power Generation | Boiler water chemistry sampling loop size changes; steam condensate line tapping | 1/2" × 3/8", 3/4" × 1/2" |
| Semiconductor | Gas distribution network OD step-downs; process gas sub-distribution headers | 1/4" × 1/8", 3/8" × 1/4" |
| Food & Beverage / Pharma | Hygienic instrument loop size transitions; CIP sampling connections | Metric 10 mm × 1/4" frac. |
| Shipbuilding & Offshore | Hydraulic sensing line connections to manifold ports of different bore size | 1/2" × 3/8", 3/4" × 1/2" |
Specify both tube ODs | Fractional · Metric · Mixed | SS 304 · SS 316 · Brass · Special Alloys | ISO 9001:2015 certified
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