Metal Detectable Safety Knife Boxer- 800M The Perfect Cutter for Cardboard and More The B800M “Box Cutter” metal detectable safety knife is a revolutionary and unique breakthrough in the field of safety knives. It is directly targeted at the most common uses for knives - the cardboard box. The B800M incorporates the spring-loaded Vari-Guard (with spring release leveler), which protects and retracts when knife is in use. For added safety the B800M comes with Security Key to prevent blade change by workers the production or process room floor. These knives are also ambidextrous for use by everyone.