Abstract: The disclosure herein describes a sealing device for a use in a sealed double glazed window assembly consisting of a pair of glass sheets arranged in spaced parallel relationship to form an air space therebetween and of a spacing unit disposed between the inner marginal edges of the glass sheets. The device comprises a flexible plug that fits into holes made in the spacing unit to allow a gas to be injected into the space between the sheets. A blind rivet is provided within the plug and when an outward pull is exerted on the rivet, an expansion of the plug results to thereby sealingly contain the gas injected between the glass sheets.