ABSTRACT
There are special forms of nuts, called inserts, which are frequently used to provide threaded holes in plastics, in both open and blind locations. They include nonthreaded types for lightly loaded applications as well as self-tapping, expansion, boss-cap, solid bushing, molded-in, and ultrasonically inserted versions. These inserts are generally for use with standard machine screws. Inserts are conventionally categorized by method of insertion used. They are divided into two major classes: those that are inserted into the mold and are “molded-in” and those that are installed after the molding operation is completed. Expansion inserts are available in two main types: cone spread, one-piece inserts and two-piece units having a cylindrical spreader that is forced down into position inside the bottom of the internally threaded insert, thus expanding it. Cap nuts are designed to allow higher torque with thin-wall bosses. They fit over the top of the boss. Ultrasonic insertion is another method of providing low stress assemblies.
