When screws or bolts are threaded directly into plastic components, failures can occur due to stripped threads or plastic creep. (When plastic is exposed to static mechanical stresses or elevated temperatures, it can move or deform.) Threaded inserts provide serviceable threads for situations when joint strength and the ability to assemble and disassemble without degrading the components are required.
The two most common methods of installing threaded inserts are thermal and ultrasonic. But, they’re not the only methods. They can also be pressed in, molded in, and even screwed in via self-tapping threads. However, installation of inserts after molding reduces costs by shortening molding time. Post-mold installation also reduces the chance of scrap and mold damage resulting from dislodged inserts.