The Swiss Tech 18mm blades are made with SK5 steel for ultimate durability and sharpness. Blades fit most 18mm snap-off knives. Pack include 5 pieces. This blades are designed to minimize risk of cutting injury and protect contents in cartons and packaged goods. heavy duty SK5 steel utility blades stays sharper, longer life than standard carbon blades. Swiss Tech 18mm Blades are engineered to fit Swiss Tech and most standard utility knives..Talented design allows the blade to extend further to achieve deeper cuts and the application of cutting dry wall, insulation etc.