These are the duct knives you want. Unbeatable quality, durability and price. Comfortable ergonomic, molded handle developed specifically by Klenk Tools for use on this Duct Insulation knife. Klenk dual duct/insulation knives are carefully crafted to be the sharpest, longest lasting knives in the industry. Made with the highest quality and durability in mind. Klenk is the original dual sided serrated duct knife and still the best knife of it's kind.