Trapezoid safety knife replacement blade helps reduce injuries in the workplace. Fits Olfa retractable Safety Knife models SK-4 and SK-9, and Retractable Auto-Lock Utility Knife (UTC-1). Each blade features 2 cutting edges. 10 blades per pack. The blades are made of high-quality Japanese grade carbon tool steel and designed for unparalleled sharpness and superior edge retention.