A system for sealing a space (16) between an inner wall (6) of a tubular opening (7) and at least one tube (17) or duct at least partly received in the opening (7), wherein the system comprises at least two segmental longitudinal parts (1) for forming a sealing plug (5) which can be received in the said space (16), wherein the longitudinal parts (1) are each provided with an outside (2) provided with a number of outer ribs (3) for realizing, in use, contact surfaces (4) closed upon themselves between the sealing plug (5) and the inner wall (6) of the opening (7), and wherein, further, each of the longitudinal parts (1) is provided with an outer collar (9) intended to be placed against an outer edge of the opening (7) in use, and wherein, further, the outer ribs (3) each substantially have the shape of a sawtooth (11) with rising surface (12).