More corrosion resistant than 304 stainless steel screws, these 316 stainless steel screws have excellent resistance to chemicals and salt water. Serrations under the head grip the material surface for mild vibration resistance, and the flange distributes pressure where the screw meets the surface, eliminating the need for a separate washer. Head height includes the flange. Length is measured from under the flange. Comes with 1 O-Ring.