A gasket is a mechanical seal between two objects, typically used to prevent leakage caused by pressure, corrosion, and the natural thermal expansion and contraction of pipes. Since machined surfaces are never perfect, gaskets fill in these irregularities. Gaskets are usually made of sheet materials such as paper, rubber, silicone rubber, metal, cork, felt, neoprene, nitrile rubber, fiberglass, or plastic polymers (such as PTFE). Gaskets for specific applications may contain asbestos.
A washer is a thin sheet (usually round) with a hole (usually in the middle) and is typically used to distribute loads on threaded fasteners. Other uses include as spacers, springs (Bellville gaskets, wave gaskets), abrasion pads, pre-display devices, and locking mechanisms. Rubber washers are also used in faucets (valves) to shut off the flow of liquids or gases. Rubber or silicone gaskets can also be used to reduce fan vibration. Typically, the outer diameter of a gasket is about twice its inner diameter.
