Gerber GDC Hook Knife A True Utility Blade, the idea behind the Gerber GDC Hook Knife and its 2” stainless steel hook blade is simple: create an ultra-stealthy knife that lives on a keychain and can be used to quickly cut yourself out of a piece of clothing, seatbelt or other safety strap, should you ever get stuck in a tight spot. You’ll also find lots of ways to use the knife for many of life’s little non-emergencies. At home, put it to use opening a box or an envelope.