A fastener is a hardware device that mechanically joins or affixes two or more objects together. fasteners can also be used to close a container such as a bag, a box, or an envelope; or they may involve keeping together the sides of an opening of flexible material, attaching a lid to a container, etc. there are also special-purpose closing devices, e.g. a bread clip. fasteners used in these manners are often temporary, in that they may be fastened and unfastened repeatedly.