Capillary Tube Manufacturer & Supplier in India
Metinox Overseas is a trusted manufacturer, stockist and exporter of capillary tubes — the fine, small-bore precision tubing that carries measured flows of gas and liquid where an ordinary tube is simply too large. Drawn to tight dimensional tolerances and supplied in stainless steel, copper and nickel alloys, our capillary tubing serves refrigeration, medical, analytical-instrument and metering applications across India and the export market. Every coil and length is a natural extension of our wider stainless steel tubes range, backed by mill test certification and in-house quality control.
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What Is a Capillary Tube?
A capillary tube is a seamless or welded tube with a very small inside diameter — typically a fraction of a millimetre up to a few millimetres — engineered so that fluid movement through it is governed by the narrow bore itself. The defining feature is not the outside diameter but the precise, tightly controlled internal diameter, which creates a predictable pressure drop or a metered rate of flow. This is what sets a capillary tube apart from general instrumentation and precision tubing: here the bore is the working component.
Because the walls are thin and the tolerances fine, capillary tubes are made from clean, high-purity material and finished to a smooth internal surface. Metinox supplies them straight-length or coiled, bare or PVC-sleeved, and — where the application demands a bright, oxide-free bore — in bright annealed and electropolished condition.
Capillary Tube vs. Instrumentation Tube — the difference
- Bore is the function. A capillary tube's small ID meters or restricts flow; an instrumentation tube simply transports a pressure signal without restricting it.
- Size class. Capillary tubing runs far finer — down to sub-millimetre ID — where the instrumentation tube usually starts at ¼" OD and above.
- Tolerance. Capillary tubes are held to tighter ID and wall tolerances because a small bore variation changes flow significantly.
- Standards. Small-diameter capillary tubing is commonly produced to ASTM A632, ASTM A213/A269 and, for medical needle tubing, ISO 9626.
Types of Capillary Tubes We Manufacture
Seamless Capillary Tubes
Cold-drawn seamless capillary tubes have no weld line, giving a uniform bore and the highest pressure integrity — the preferred choice for high-pressure metering, analytical instruments and demanding fluid systems. Produced to ASTM A213 / A269 / A632 in austenitic grades.
Welded Capillary Tubes
Precision welded and welded-drawn capillary tubes offer excellent dimensional consistency and economy for larger volumes and standard-pressure duties. Our welded small-bore tubing is bright annealed to normalise the weld and deliver a clean, corrosion-resistant bore.
Copper Capillary Tubes
Soft-annealed copper capillary tubes are the classic metering / throttling element in refrigeration and air-conditioning circuits, supplied in long coils for easy routing.
Capillary Tube Material Grades
Material selection is driven by the fluid, temperature and corrosion environment. Metinox stocks and produces capillary tubing across the following grades — each linked to its full specification page:
- SS 304 / 304L Capillary Tube — general-purpose, cost-effective, good corrosion resistance.
- SS 316 / 316L Capillary Tube — the workhorse for medical, marine and chloride-bearing service; superior pitting resistance.
- SS 321 / 321H Capillary Tube — stabilised grade for high-temperature and thermal-cycling duty.
- Duplex 2205 Capillary Tube and Super Duplex S32750 — high strength with excellent stress-corrosion resistance.
- Monel 400, Inconel 625 and Incoloy 825 — nickel-alloy capillary tubing for aggressive, high-temperature chemical service.
- Titanium & special-alloy capillary tubes — for weight-critical and highly corrosive applications. See also our special alloys range.
Capillary Tube Dimensions & Specifications
Typical size envelope for Metinox capillary and small-bore precision tubing. Custom OD, ID and wall combinations are produced to order — share your drawing for an exact quotation.
| Parameter | Range / Detail |
|---|---|
| Outside Diameter (OD) | 0.30 mm to 12.70 mm (0.012" to ½") |
| Inside Diameter (ID) | From 0.10 mm — held to tight tolerance |
| Wall Thickness | 0.05 mm to 1.5 mm (thin-wall precision) |
| ID / OD Tolerance | Precision class, to customer drawing |
| Length | Straight lengths or coils (coiling standard for fine sizes) |
| Type | Seamless / Welded / Welded-drawn |
| Condition | Soft annealed, bright annealed, electropolished |
| Supply Form | Bare, PVC-sleeved, capped ends |
| Mill Test Certificate | EN 10204 3.1 / 3.2 |
Bright Annealed & Electropolished Bore Finishes
For refrigeration, analytical and ultra-clean fluid service, the inside surface of the tube matters as much as its dimensions. Metinox supplies capillary tubing in ASTM A269 bright annealed condition for a clean, oxide-free bore, including 316L BA tubing and 304 bright annealed tubes. To understand which finish suits your duty, see our guides on bright annealed instrumentation tubing selection and surface roughness (Ra) — BA, AP & EP finishes explained.
Capillary Tube Applications
Capillary tubing sits inside precision equipment across many sectors. Common uses include:
- Refrigeration & HVAC — capillary tube as the expansion / metering device in cooling circuits and refrigerators.
- Medical devices — hypodermic needles, catheters, probes and diagnostic instruments (ISO 9626 needle tubing).
- Analytical instruments — gas & liquid chromatography, sampling lines, mass-spectrometer inlets.
- Process instrumentation & metering — flow restrictors, pressure snubbers and sensor lines in oil & gas and petrochemical plants.
- Chemical processing — dosing and sampling in chemical & refinery service.
- Aerospace, electronics & thermocouples — fine fluid lines, sheathing and heat-transfer elements.
For seawater and offshore duty, our marine & offshore grades — 316L, duplex and copper-nickel — are the usual choice.
Global Capillary Tube Supply & Export
From our India base, Metinox exports capillary and precision tubing worldwide, with strong service across the Gulf and beyond — UAE, Saudi Arabia, Oman, Qatar, Kuwait and Bahrain.
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Frequently Asked Questions
A capillary tube meters or restricts the flow of a fluid through its small, precise bore. It is used as the expansion device in refrigeration and air-conditioning, as needle and probe tubing in medical devices, and as sampling and flow-restrictor lines in analytical instruments and process metering.
A capillary tube's small internal diameter is the working part — it controls flow or pressure drop. An instrumentation tube simply carries a pressure signal without restricting it and is generally ¼" OD or larger. Capillary tubing is finer and held to tighter ID tolerances.
Most commonly SS 316/316L and SS 304/304L for corrosion resistance, and soft copper for refrigeration. For aggressive or high-temperature duty, Metinox also supplies duplex, Monel, Inconel, Incoloy and titanium capillary tubing.
Our capillary tubing starts from around 0.30 mm OD with inside diameters down to about 0.10 mm, held to precision tolerance. Exact ID, OD and wall are produced to your drawing — share your specification for a quote.
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