Non-threaded plastic fasteners are generally classified by product families and include rivets, washers, pin fasteners, quick-operating fasteners, retaining rings, inserts, spacers, clips, harnesses, clamps, wire bundlers and ties, snap inserts, and grommets. Plastic fasteners are considered for applications where environmental, thermal, optical, weight, chemical, and electrical properties are a significant consideration for end use. Plastic materials meet a broad spectrum of design requirements — strength, rigidity or flexibility, heat, low temperature, chemical and corrosion resistance, sealing, toughness, good electrical properties, and light weight. Common plastic fastener materials are often less costly than their metal counterparts.