Which type of screw is most suitable for use on harder metals?

Thread-cutting screws are specifically designed to create threads in harder materials during installation. They have cutting edges that remove material as they are driven into the metal, allowing them to form precise threads that securely anchor the screw within the harder substrate. This ability to cut and shape the material makes them particularly effective for use in applications involving steel and other tough metals.

In contrast, thread-forming screws displace material rather than cutting it, which makes them more suitable for softer materials like plastics or softer metals. Self-tapping screws can also be used in harder materials but are primarily designed for applications where a pre-formed hole is not present; however, they may not perform as well as thread-cutting screws in very hard metals due to their design. Hexagon head bolts are typically used in assemblies where high torque is required, but they are not designed for cutting threads into hard materials like the thread-cutting screws.