Abstract: The external cassette casing of a narrow-gauge film cassette with film spools arranged coaxially to each other is closed on five sides and only open on the side opposite the film window. The base of the cassette casing is provided with a hole opposite the dog-cassette opening. A screw plug is placed through this hole, this plug engaging in a corresponding thread in the hollow bearing pin of the film take-up core with its thread shank and projecting slightly beyond the open worked end of the bearing journal with the lengthened part of the shank.