SEMS screws have an indented hex head with a recessed phillips drive and a captive (permanently attached) flat washer. Length is measured from underneath the head, including the washer.
The black oxide coating per MIL-DTL-13924, Class 4 on 300 series corrosion resistant steel meets 96 hours of resistance in a 5% salt spray (fog) test in accordance with ASTM B117. We recommend using stainless steel installation tools to prevent extraneous rust.
