A screw connector includes a first connector with a first lumen and an outside thread, and a second connector with an elastically deformable nut and an inside thread. The outside thread has a first formation and the nut has a second formation, the second formation is a recess in the base of the nut, and the inside thread and the outside thread are configured for mutual connection. The nut is configured for deformation by the first formation in a first angle-of-rotation range without the first formation engaging in the recess, and the inside thread, the outside thread, the first formation, and the recess are configured for engaging the first formation when the inside and outside threads are connected in a second angle-of-rotation range. The screw connector has a half-open sterilization position in the second angle-of-rotation range. In another range, the screw connector may be tightened to be gas-tight and/or liquid-tight.