is a heavily built rotary mower. Typically these mowers attach to the back of a farm tractor using the three-point hitch and are driven via the Power take-off (PTO). It has blades that are not rigidly attached to the drive like a lawnmower blade, but are on hinges so if the blade hits a rock or stump, it bounces backward and inward, and then centrifugal force makes it go outwards again.   The rotary blades are not sharpened in the same way as a conventional mower blade. They are usually quite dull so they whack through dense plant growth, where a sharp blade will get stuck or slowed down. The blades are very heavy, up to an inch thick, so the centrifugal force pulling out is stronger than the forces of the vegetation bouncing in. They are made of heat treated high carbon steel that can withstand strikes with hard objects such as rocks and stones.