Safety knife hook replacement blade helps reduce injuries in the workplace and protect your cutting surface. Great for cutting shrink-wrap and nylon straps. Blades manufactured using OLFA multi-step production process for superior sharpness and blade retention. For Retractable Safety Knife (SK-4) and Retractable Auto-Lock Utility Knife (UTC-1). Each blade features 2 cutting edges. 5 blades per pack.