These screws are prepared to be used on chambers and parts in high-vacuum systems after being cleaned and double-bagged in an ISO Class 5 (Fed. Std. Class 100) clean room. Because 18-8 (SS 304) stainless steel releases gas more slowly than other metals, your system can attain higher vacuum levels. Over time, wear is decreased by the lubricating effect of silver plating on screws. Under the head, the length is measured.