plain washer,with different sizs , materials, finishes and standards . plain washerstandard : JIS , DIN . AISI, GB .material : carbon steel , ... stainless steel , alloy steel .finish:plain,black oxide , blue zinc ,yellow zinc , black zinc , nickel ... DIN, ANSI (IFI), BS, JIS, etc.The material could be brass , aluminum , carbon steel , alloy steel , stainless steel , zinc ...