METU-FORM laser-welded and/or MIG-soldered, liquid and oil-tight cross pieces made of galvanized steel or stainless steel (V2A / 1.4301 / 304). Two versions: with "Parallel" flanges formed directly from the duct itself (diameters 80 to 1000 mm Ø, connection with SRX joining clips), or "plain " (without a flange, diameters 80 to 200 mm, connection with MUX Overcollars). The air-tightness exceeds the highest-class D according to the norm DIN EN 12237. Tightness class ATC 1 (EN 16798-3). No ATEX / EX certifications.