Abstract: The invention relates to a washer having a screw-thread formed in a central bore thereof to enable the washer to be screwed onto a screw-threaded member the washer being adapted for tensioning itself against a surface when screwed up against the surface for increasing friction between the washer and the screw-threaded member; and at least one portion of the washer providing an inwardly extending edge frictionally engageable with said surface when the washer is screwed up against said surface for inhibiting unscrewing of the washer relative to the surface.