A coupling system for a closed fluid transfer system includes a coupling member that features a coupling member housing. The coupling member housing includes a housing portion that at least partially surrounds a sealing member receptacle in an axial direction with respect to the longitudinal axis and which includes a coupling member housing threaded portion on the inner surface facing the sealing member. The coupling system also includes a mating coupling member for coupling with the coupling member. The mating coupling member includes a mating coupling member housing that has a mating coupling member guiding structure. The coupling member housing threaded portion of the coupling member is configured such that the mating coupling member guiding structure and the sealing member receptacle structure are jointly and movably guided, in particular in a predetermined positional relation to each other, by the coupling member housing threaded portion.