The gasket (GASKET) is a mechanical seal between two objects, usually used to prevent the pressure, corrosion, and natural expansion of the pipeline between two objects. Because the machined surface can not be perfect, the use of gaskets can fill the irregularities. Gaskets are usually made of flaky materials such as pads, rubber, silicone rubber, metal, cork, felt, neoprene, nitrile rubber, fiberglass or plastic polymers (such as Teflon). Gaskets for specific applications may contain asbestos. Washers (Washer) are a flaw (usually in the middle) of a sheet (usually round) that is usually used for allocating load thread fasteners. Other uses are as spacers, springs (Belleville Gaskets, wave washers), wear resistant pads, pre display devices, locking devices. Rubber washers are also used on taps (valves) to cut off flowing liquids or gases. Rubber or silicone gaskets can also be used to reduce fan vibration. Usually the outer diameter of the gasket is about twice times the inner diameter.