Gaskets are a shaped piece or ring of rubber or other material sealing the junction between two surfaces.

Gaskets are typically made from a material that is somewhat yielding so that it is able to deform and tightly fill the intended space, including any slight irregularities.

Some (piping) gaskets are made entirely of metal and rely on a seating surface to accomplish the seal. This is typical of some "ring joints" (RTJ) or some other metal gasket systems

Pipe Fittings Gaskets