Keychain Knife with Retractable Razor Blade&mdash;Best Small Box Cutter/Penknife Smaller than Xacto Knife Three, 2 inch keychain knives each with a half inch razor blade which is smaller than an Xacto knife for quickly cutting open boxes. Handy key chain knife with small box cutter/penknife to put with your keys for easy transportation. Small retractable razor blade size feels like just another key on your key chain. Looks and feels like a key, but is a highly efficient small box cutter knife. Super sharp penknife/pocket knife with a lock in place to keep it from opening while in your pocket.