A large area washer with a perforation (2) through which a fastener passes has a peripheral border (4) which forms the peripheral limit (3) and which is constructed from one or more longitudinal steps or curves. Individual sections (6) of the peripheral border (4) are set back in the longitudinal direction of the latter from the sections (5) in a plane parallel to, and at a distance from, said sections. The transitions (7) between the mutually offset sections (5, 6) of the peripheral border (4) are curved or sharp-angled.This type of washer can be made of relatively thin-walled material but is nevertheless suitable for use in unmatching devices.