Safer to use with comfortable molded handles. Male and Female Shiplap Knives for 1” (25 mm) and 1-1/2” (38 mm) ductboard can be used on closed duct sections. Duct Knife features a rounded scoring edge to cut fiberglass without tearing skin. Plus, Malco’s No. FG1 Hole Cutter and a special 1-1/2” (38 mm) blade No. KBHC are available separately for creating flex duct take-offs.