This is the Combat Commander boot/shoulder knife by United Cutlery. It measures 9 3/8″ (239mm) overall. The black coated double edged AUS-8 stainless steel blade is 5 1/8″ (131mm) long with a blood groove on each side.
The handle is black injection molded impact resistant TPR with a brass lanyard sleeve and a full guard. Includes a black nylon belt/boot sheath with a removable shoulder harness.