Threaded and nonthreaded conventional plastic fasteners have the same dimensional thread class and fit standards as those for metal fasteners. Sizes range from 00 to in. in diameter and in lengths up to 6 in. Threaded plastic fasteners include bolts, screws, rods, studs, and nuts.
Nonthreaded 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.
Plastic fasteners can have special functions, in addition to being available in standard shapes. Integral color, special undercuts, and molded-in metal inserts are a few of the possibilities. Assembly can be simplified when a single plastic fastener replaces several metal components.
A plastic fastener must be evaluated not only on the material to be used, but on the intended application as well. Physical, mechanical, thermal, environmental, and electrical properties must be considered. Interaction of the plastic with other materials is also a potential problem.
In the evaluation of plastic for use in a fastener, the designer should be aware that plastics' properties may be altered by alloying, varying the processing techniques, or adding fillers, lubricants, or reinforcing materials.
Plastic fastener materials can have a glass or metallic filler added to the base resin to improve strength, stiffness, useful temperature range, and specific gravity. Therefore, the designer should consult his fastener supplier for assistance in selecting the best material and fastener for each application. Plastic fasteners, like most specialty fasteners, are often available in custom versions.
In addition, plastic fasteners may be able to combine the advantages of their metal counterparts with advantages of their own. For example, several plastic fasteners are designed similarly to standard blind rivets. However, plastic permits several variations on this theme. Available designs can be inserted by hand or removed and reused. Drive-pin, threaded-pin, and pull-mandrel styles are available.
Advantages of plastics in these cases include the potential for use in soft materials, especially when fasteners have a broad bearing surface; a wide range of material colors; and elimination of galvanic corrosion. In addition, plastics are nonconductive, making them useful in electrical and electronic applications.