X-ACTO Zirconium Nitride X-Life 500pc XZ511 No 11 Knife Blades. The gold hue on teh cutting edge is a zirconium nitride coating. These are on average 7-10 times sharper than other X-ACTO blades. The coating also adds significant strength to the blade itself, particularly the tip. For delicate, precision cutting, detailing, trimming and stripping. Paper, plastic, balsa, and bass wood. Fits 1/4 inch Type A X-ACTO or Excel Handles.