Tightening torques for cutting-ring fittings: L and S series

DIN 2353 and DIN EN ISO 8434-1 standardize the geometry of the fitting, the 24-degree cone, the threads and the cutting ring, but not the tightening torque. That is why every manufacturer states its own values, and why the tables diverge. A tightening torque depends on lubrication, surface and coating (friction-coated nuts about 30 percent lower), material (aluminum bodies at least 30 percent lower), sealing form and connection type. Every catalog marks its Nm values explicitly as approximate only.

More important is separating the two force points. The stud end, that is the port thread, is tightened with a torque wrench; the tables further down are for it. The tube-side union nut with the cutting ring is assembled not to a torque but by turns. The sizes and series themselves are explained in the article DIN 2353: series LL, L and S.

The following values apply to the stud end of the light series, for steel phosphated and oiled. Form E is the soft seal with an elastomer sealing ring (ISO 1179-2 or ISO 9974-2), Form B the metallic sealing edge (ISO 1179-4 or ISO 9974-3). For aluminum bodies reduce by at least 30 percent.

For the same tube nominal size, the heavy series carries larger threads and higher torques. For the large sizes with 800 Nm at the G 1 1/2 stud you work with a correspondingly long torque wrench; at very high torques a hydraulic torque wrench comes into play.

The cutting ring itself is not tightened to Nm. DIN 2353 prescribes a turn-controlled assembly per DIN 3859 for it: you count the turns of the union nut, because the ring has to cut a defined distance into the tube, and that distance is reproducible through the turn, not through force. Parker deliberately states no component-specific Nm values for the metallic cutting ring, only assembly torques on request. How many turns each phase needs is set out step by step in the article Assembling a cutting-ring fitting.

So why do you still find Nm tables for the tube side? Because two other connection systems use the same 24-degree cone but seal differently and therefore publish their own tightening torques. The metallic profile ring (for example Walterscheid) and the 24-degree DKO soft seal with O-ring (for example STAUFF) are separate connection types, not a brand contradiction of the cutting ring. Anyone who transfers the values of one system to the other, or even averages them, assembles wrongly.