Screws

Screw fasteners, usually made of metal, are fasteners with male external threads (helical surface ridges) that engage with the female internal threads in the components they are fastening.

A defining feature of screws is that they are often self-threading or self-tapping: they have a sharp end that cuts into the surface of the component; when the screw is rotated, it cuts out the female internal thread into the component and allows the connection to be made. Screws are often standalone fasteners, as they join with the component itself.

Screws are similar in function to bolts, but bolts are not usually self-threading; they typically have blunt tips, and female threads in the components must be made via other means.

Confusingly though, some fasteners that are technically screws have, through usage, been labelled as bolts (and vice versa).