Swagelok SS-12M0-6 Metric Tube Union, 12 mm Tube OD

Metric tubing is common in instrumentation packages built to European and Asian practice, and 12 mm is one of the frequently used sizes. The Swagelok SS-12M0-6 is the straight union for 12 mm outside diameter tube, with a metric Swagelok tube-fitting end on both sides in 316 stainless steel. Its fractional-size relatives, such as SS-810-6 for 1/2 in., use the same design but are not interchangeable with metric tube.

Technical specifications

Metric versus fractional tube

A 12 mm tube is 0.472 in. in outside diameter, so it does not fit a 1/2 in. (12.7 mm) fitting and a 1/2 in. tube cannot seat in a 12 mm body. The catalog guards against this with a visible marking: metric tube-end bodies have a stepped shoulder on the body hex, while shaped metric fittings (elbows, tees, crosses) are stamped MM and have no step on the forging. Fractional stubs carry no shoulder. The same catalog page tells installers to check for these identifiers.

Compared with the 1/2 in. union SS-810-6 at 2.02 in. (51.3 mm), the 12 mm union is the same length to within rounding, with a 22.8 mm nut dimension and a 9.5 mm opening.

Ordering

SS-12M0-6 reads SS for 316 stainless, 12M0 for 12 mm tube and 6 for a union. Other 12 mm shapes follow the same pattern, such as 12M0-9 elbows, 12M0-3 tees and 12M0-4 crosses, and the connector SS-12M0-1-8 for a 1/2 in. NPT thread. Metric fittings also exist for other tube sizes from 2 mm to 50 mm in the catalog.

Cleaning and packaging options are the same as for fractional fittings: CP for bagging and BQ for the special cleaning level with silver-plated front ferrule.

Tubing, pressure and installation

Use metric tubing of 12 mm outside diameter in a material at least as soft as the fitting, with a smooth, round, scratch-free surface and a wall within the catalog limits. The connection is rated to the working pressure of the tubing; find the value for your wall thickness and material in the Swagelok Tubing Data catalog.

On first assembly, seat the tube, tighten the nut finger-tight and turn it one and one-quarter turns, using the correct Swagelok gap inspection gauge for the 12 mm size to confirm pull-up. Hold the body steady and turn only the nut.

Where a 12 mm straight union is used

A straight union joins two lengths of tube of the same size in a straight line. On instrumentation skids, analyser shelters and hydraulic or pneumatic panels, the SS-12M0-6 is typically used to extend a run that is longer than a single tube length, to join a new section to an existing line during modification, or to create a break point in a line that may need to be opened for maintenance. Because both ends are 12 mm metric Swagelok tube-fitting ends, the union only makes sense where the whole run is 12 mm metric tube. Where the line changes to fractional tube or to a threaded port, a different fitting from the same catalog is required.

Selection checklist before ordering

• Confirm the tube is metric 12 mm OD, not 1/2 in., by measuring it and by checking the project tube specification.
• Check that the tube material and wall thickness are suitable for the fitting and that the system pressure is within the working pressure of that tubing, using the Tubing Data catalog.
• Confirm that 316 stainless steel suits the process medium and the external environment.
• Decide whether standard cleaning and packaging SC-10 is enough, or whether the CP or BQ options are required by the project.
• Keep metric and fractional fittings in separate, clearly labelled stock to avoid mixing on the work bench.

Installation and inspection practice

Cut tube square and deburr it, then make sure the tube end is clean and free of scratches in the area that seats in the fitting. Insert the tube fully until it bottoms in the body before tightening. Follow the one and one-quarter turn pull-up described above, and use the correct gap inspection gauge for 12 mm to confirm each new connection. Mark the nut and body after tightening so that inspectors can see which joints are complete. For later disassembly and reassembly, follow the Swagelok catalog guidance for remade connections.

Service in Gulf process plants

Oil and gas, desalination and utility plants in Oman expose tubing to high temperatures, sand, and salt-laden coastal air. Keep tube ends protected and clean until installation so sand does not enter the line, and clean the outside of the fitting before inspection so that the identification shoulder and the pull-up mark remain visible. Include unions in routine leak checks on instrument lines, particularly after start-up, thermal cycling or vibration from nearby machinery.

What to state in your RFQ

List the part number SS-12M0-6 and the quantity, the tube material and wall thickness used on the project, and any cleaning or packaging requirement such as CP or BQ. If other 12 mm shapes such as elbows, tees or connectors are needed on the same line, list their full part numbers on the same enquiry so they can be checked together.

Documents and quotation

Attached for download is the official Swagelok catalog MS-01-140, which carries the dimension and pressure-rating tables behind this page. Quote requests are handled against the exact code, so list SS-12M0-6, the quantity and your cleaning or packaging needs.

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