Blech
Sheet metal screws (sometimes called "sheet-metal self-tappers", or P-K screws from the brand name "Parker Kalon" - who pioneered the manufacture of, but did not invent, these screws) are a type of self-tapping screw despite the thread created in the sheet of metal being small. Pan-head PK Self-tapping screws are common in electrical equipment, while flatter-headed truss or flat countersunk headed self-tapping screws are more common in aviation applications.