Straight unions
Threaded fittings
Straight unions join two precision steel tubes of equal size directly to each other. The body carries a cone, a union nut plus a cutting ring at both ends; there is no stud thread towards a housing. 106 versions cover 25 tube outside diameters, from 4 LL (M8x1) on pilot lines up to 42 L (M52x2) on main runs, rounded out by the heavy series up to 38 S (M52x2).
Only the tube series matters here, because it fixes cone angle, ring shape as well as the permissible pressure. The extra light series is stated at 100 bar on tube 6 LL, the light series at 160 bar on tube 42 L, while a version made for tube 16,75 mm reaches 315 bar. Zinc plated steel plus stainless steel 1.4571 are available, each of them also as a bare body shipped without nut or ring.
Equal tube diameter does not imply an equal fitting: an 8 mm tube exists as 8 LL (M12x1), 8 L (M14x1,5) as well as 8 S (M16x1,5), each one taking its own nut plus its own clamp ring. The marking on the tube, alternatively the size across the existing union nut, identifies the series beyond doubt. Within one series the spanner size grows along the diameter while the permissible pressure drops, so the slim heavy series lines carry the highest figures.
Extending as well as splitting rigid tube runs on power packs, presses plus machine tools, wherever a line cannot be laid in one piece. Equally common in repair work: a damaged length is cut out, then replaced through two unions plus a fitted piece of tube. Further use in plant building, cabinet piping, lubrication as well as cooling lines, on test rigs where series LL through S run side by side.
