The invention relates to a screw connector for a medical tube system, comprising a first connecting element having a first lumen and an outer thread, and a second connecting element having an elastically deformable nut with an inner thread, wherein the inner thread and the outer thread are configured such that they can be screwed together, and wherein the outer thread has a first moulding and the nut has a second moulding, said second moulding being a recess in the thread base of the nut. The inner thread and the outer thread are designed for mutual screwing, and the nut is designed for elastic deformation via the first moulding in a predefined first rotation angle range, without the first moulding engaging with the recess in the thread base of the nut, and the inner thread and the outer thread and the first moulding and the recess in the thread base of the nut are designed for the engaging of the first moulding with the recess in the thread base of the nut, when the inner thread and the outer thread are screwed together in a predefined second rotation angle range, whereby the screw connector has a half-open sterilising position in the predefined second rotation angle range. In a further rotation angle range, the screw connector can be screwed shut in a gas- and/or liquid-tight manner.
