C121 needles are compatible with all regular tag guns. The cutting blade is built in to these needles, which means the base of the needle has a sharp knife to separate the fasteners from their clips.Every time you replace the needle, you get a new sharp knife as well. Total Needle Length (A) : 31 mm Total Shaft Length (B) : 22 mm Needle Shank Length (C) : 11 mm Needle Shaft Diameter (D) : 2 mm Maximum Thickness of Fabric (E) : 9 mm For above detail description Please check all Photos.