The Megasafe is an ergonomically designed heavy duty cutter that is made with an aluminum handle that allows both left and right handed users to easily perform general purpose cutting tasks. Unlike earlier versions of safety knives, the Megasafe features Martor's "smart knife technology" allowing the blade to automatically retract when the blade loses contact with the material being cut. The blade will STILL RETRACT even if the user leaves the slider in the forward position. This cutter features an easy, tool free blade change and can handle a straight or hook blade. (This model comes standard with a 0.63 mm trapezoid blade number 99.70) "GS - TESTED FOR SAFETY"