These specially made gaskets are available in Single and Double size (Square and Rectangular), and are used when fitting dimmers, switches and sockets to freshly plastered, or painted walls. The chemicals in paint and more so plaster, reacts with the plate and tarnishing of the plate can occur. If this happens it breaks the warranty of the product bought. So for very little money, buy these and save yourself the hassle and expense replacing the products you have bought. Please note sometimes due to moisture in the air it could take considerably longer (up to 1 year) for the plaster to fully dry out. Afterwhich, just loosen screws of product, and pull gasket free. Can be re-used if removed carefully.