For reaching hard-to-get-at screws, the ratchet offset screwdriver is used, especially where leverage is required. The ratchet drive reverses instantly for clockwise or counterclockwise rotation. The blades are made of machined ground and hardened tool steel. Recessed head screws, which are used extensively on office machines and in machine shops, usually have a hex-shaped (six-sided) recess. To remove or tighten this type screw requires a special wrench that will fit in the recess. This wrench is also called a hex wrench.