This plastic prismatic key transfers torque between two rotating components within the reel drive assembly of a grain harvester header. It fits into a machined slot on the shaft and the mating hub, preventing relative rotation while allowing the drive to transmit power to the reel. A worn or sheared key causes the reel to slip or stop turning, leading to uneven crop feeding into the auger. The plastic material is selected to act as a sacrificial element, protecting more expensive driveline components from damage in the event of a sudden overload. On installation, ensure the key seats fully in the slot and that the mating hub is aligned before tightening the retaining hardware.