This moving knife is the cutting element mounted on the straw chopper rotor. It swings on its pivot point as the rotor turns, impacting the crop stream against a stationary counter-knife to reduce straw length. Each knife is free to pivot, which allows it to deflect if a foreign object enters the chopper, reducing the risk of damage to the rotor assembly. Over time, the cutting edge wears and the knife becomes blunt, leading to ragged straw and higher power draw from the chopper drive. The manufacturer machines the pivot hole and the cutting edge profile to match the original assembly geometry, so the knife swings freely without binding on the mounting pin. When replacing, inspect the pivot pin and the counter-knife for wear, and replace all knives on the same rotor to maintain balanced cutting.