The frame for these manual-locking carabiners are NFPA certified with a  screw gate mechanism. These "Equal-D" carabiners are large, but light weight and comfortable enough so that it fits in one hand without being difficult to handle. This manual-lock design is representative of US Rigging’s pledge to assemble only the best carabiners in the world. The Screw Lock Large D Carabiners is made from zinc plated steel to reassure durability even when used in the most severe climates.