A seal for a work cylinder operated with pressure fluid, through which cylinder an axially displaceable coupling element connected with the work cylinder, particularly a pull means, is extended in a fluid-tight manner from the inside of the cylinder. To obtain a better sealing of the inside of the cylinder under all possible operating conditions, particularly when using coupling elements developed as pull means of a cross-sectional shape other than circular, the seal is comprised of a single cup-shaped piece, the bottom surface of the seal being provided with a cuff which tapers conically in axial direction towards the cup-shaped inside of the seal. The cuff is provided with a sealing opening which permits the passage of the coupling element therethrough. The seal is provided with a sealing ring on the outer periphery in the region of the open end.