The Van Mark TrimCutter #3017 is used to slit aluminum, steel and copper for residential siding, roofing, window and gutter installation right on your Van Mark Brake. The TrimCutter rides on the top lock bar of the Mark I, Mark II TrimMaster, Mark IV Industrial and Metal Master Series brakes. Designed to protect Van Mark brakes from potential hinge damage from use of utility knives. The rotary knives make consistent cuts giving factory edges every time. Its unique 4 point track bearing system and low profile grip ensures the tool does not ride off the tracks. Van Mark makes the strongest, most durable and highest quality jobsite tools in the industry.