ROBERTS Pro Dual-Depth Carpet Knife is a must have for carpet installers. Expertly designed, this knife provides tool-free, easily adjustable blade depth options: 9/16� or 13/16� to accommodate different carpet back thickness. Ideal for use with round- or square-end slotted blades, the Pro Dual-Depth Knife features SWIVEL GRIP, a patent-pending blade spindle that stores most brands of 10-packs and up to 20 single blades. The molded comfort grip and ergonomic design increase leverage and pulling power. The magnet on blade holder holds blades in position while open; Knife cavity fully butterflies for full access and easy blade change.