A gasket is a mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression. they are a significant part for the machineã¢s accuracy & design. a gasket is a mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression. they are a significant part for the machineã¢ï¿½ï¿½s accuracy & design.