The Vestil Positive Lock Plate Clamps grip a sheet until the release ring is pulled. The serrated gripper is constructed of hardened steel. Forged head and gear. Safety factor is 2 to 1. Durable blue paint finish. Designed to meet ASME B30.20 standards. Not designed for use on stainless steel or aluminum plates. For use with materials with a surface hardness to 30 RC (300 HB). Available in 2,000-lb., 4,000-lb. or 6,000-lb. capacity models.