Abstract: Disclosed is a plastic sealing device comprising a hollow, bottomless cubic body and a sealing strip integrally connected to and extending from said cubic body. The sealing strip has an arrowhead-shaped end, and in use, the arrowhead-shaped end of the strip is inserted in the slits of the hollow cubic body, and is pulled out of the cubic body, thus passing therethrough and closing the open bottom of the cubic body. After passing through the apertures of an object to be sealed, the arrowhead of the strip is inserted in a slit in the top plate of the cubic body until it is caught by catch means within the cubic body. The structure of the sealing device is conveniently amenable to plastic injection moulding and mass-production.