The Stanley 99 Classic Retractable, Quick Change Retractable, and Instant Change Utility Knives all come equipped with three heavy duty blades and a three-position retractable knife blade. The 99 classic also features flexibility that has an interlocking nose to hold the blade safely and securely. Quick Change knives from Stanley also showcases an integrated string cutter for use even when blade is retracted. The Instant Change utility knife has a tool-free push-button blade change and has a strong, durable construction that combines a cast metal core with bi-material soft panels for a sure grip. Stanley also manufacturers replacement 11-921 heavy duty utility knife blades. These blades are sold in a standard carded 5-Pack or a dispenser of 100 blades that can be easily mounted on a wall.