The thread of these screws is narrower than the wood ones and the edges are sharper because the metal is stronger. They allow to join metal with metal, metal with wood, metal with plastic or metal with other materials.

In the case of self-tapping screws, a hole has to be made in the base material first and then they are threaded. The pre-drilling has to be a little smaller than the diameter of the screw so that it threads well.