Which of the following materials are thread-forming screws suitable for?

Thread-forming screws are particularly suitable for ductile materials because their design allows them to create their own threaded hole as they are driven into the material. Ductile materials, such as certain plastics and softer metals, can easily experience deformation without breaking, which is essential for the thread-forming process. These materials can accommodate the cold-working action as the screw displaces the material to form the threads.

In contrast, rigid metals, while they can sometimes be used with specific types of screws, typically do not allow for the same level of deformation that ductile materials do, making threading more challenging and potentially leading to failure. Hard metals might resist deformation altogether, making it difficult to form threads without pre-drilling. Composite materials may not provide the necessary ductility or could be damaged by the installation process, thereby limiting the effectiveness of thread-forming screws. Therefore, ductile materials are the most compatible with the function and design of thread-forming screws.