Prevent rot in roofs, decks, and outdoor posts. The rubber-backed washer in these screws keeps fluid out of fastened joints. They're made of stainless steel, so they won't degrade from chemically treated wood, such as ACQ-treated (arsenic-free) lumber. Also known as trim head screws, they exert less pressure on surfaces to curb splitting and distortion. 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.