Designed for rescue, SMC’s Locking D carabiners are state-of-the-art. With thousands of these carabiners in service, they have proven themselves reliable. The carabiner gates and screw sleeves are constructed of stainless steel for greater strength and the nuts lock on the gate to prevent jamming. These carabiners have become the choice of many mountain rescue teams and fire department rescue squads. I only have one