A screw connector for medical hose systems is configured for catch engagement in a half-open sterilization position. The connector includes a first connecting element having a first lumen and an outside thread, and a second connecting element having a second lumen, and an elastically deformable union nut having an inside thread. The inside thread and the outside thread are configured to be screwed together, with the outside thread having a first formation and the inside thread a second formation, with deformation of the nut via the first formation in a predetermined first angle-of-rotation range without engaging the second formation. The inside thread and the outside thread, and the first formation and the second formation, are configured for catch engagement of the first formation in the second formation when the inside thread and the outside thread are screwed together in a predetermined second angle-of-rotation range to provide the half-open sterilization position.
