Perma-Set Scissors; Self-Sharpening Design Maintains A Sharp Edge; Straight; Sharp-Blunt; 45mm Blade Length Perma-Set scissors have a unique design that enables them to self-sharpen as they are used. The scissor hinge is designed to provide spring tension on the two blades so, as they cut material, one blade presses against the other, sharpening the surface as they close.