Lock in for a tighter hold than typical wood screws. Serrations beneath the flat head dig into wood to secure these screws into place. Made of stainless steel, they won't degrade from moisture or chemically treated wood, such as ACQ-treated (arsenic-free) lumber. Also known as a Robertson drive, the square drive handles more torque than slotted and Phillips drives, so it's less likely to slip.

The screw drill tip acts as a built-in pilot, though pilot holes are still recommended near edges to avoid splitting. Length is measured from the top of the head.