Metric & DIN Fittings

A DIN 2353 metric tube fitting holds the tube with a hardened cutting ring that bites into the outer wall as the nut is drawn up, so anchor and seal are made at one place by one movement. The tube needs no flaring, only a square cut and a deburr. Metric port ends work the other way, sealing on an elastomer compressed into a counterbore or under a shoulder.

Engineers specify them because the machine already speaks millimetres: ISO 8434-1 (DIN 2353) tube ends, ISO 6149 O-ring ports and DIN 3852 threads arrive on European-built pumps, valves and cylinders, and forcing an inch thread into one ruins it. The trade is inventory: two series and threads close enough to inch sizes to confuse at the bench.

Where it's specified

• European-built machinery — ports and tube runs are already in millimetres
• Impulse and shock duty — the S (heavy) series pairs thicker-wall tube with a larger nut and thread at the same tube OD
• Routine plumbing — the L (light) series keeps weight and cost down where the heavier joint is not needed
• Ports that must not wedge a taper — ISO 6149 and DIN 3852 ends seal on an elastomer, so torque sets clamp load

Range and materials. Straights, unions, 45° and 90° elbows, tees, crosses, bulkheads, reducers, swivels, stud ends, nuts and rings run 6 mm to 38 mm tube OD in both series, in zinc-plated steel and stainless. Adapters convert metric ends to JIC 37°, ORFS, O-ring boss, NPT and BSP.

Ordering notes. Metric tube is called out by actual outside diameter — 6, 8, 10, 12, 15, 16, 18, 20, 22, 25, 28, 30, 35 and 38 mm — so measure it rather than converting a dash size. Confirm the series first: L and S parts at the same tube OD carry different threads and nut sizes and will not assemble, the most common error on metric orders.