"The MTD 711-04416A Shaft-Hexagonal Drive is a tough steel component used on MTD lawn products. In a list of things that it does, it works as an axle through which power from the motor gets to limbs like the wheel or blades. Its hexagonal design offers a close fit a high degree of accuracy, and a high clamp load to minimize slippage during operation. Made from high-quality steel, this... https://www.wholetoolbox.com/mtd-711-04416a-shaft-hexagonal-drive-steel