This screw secures a disc harrow blade or scraper assembly to its mounting hub. It passes through the blade center and threads into the hub, clamping the components together under the specified torque. A loose or missing fastener allows the blade to shift on the hub, causing uneven disc spacing and accelerated wear on the hub bore. The mushroom-shaped head provides a broad bearing surface that distributes clamping force evenly against the blade. On reinstallation, clean the threads and the hub bore, then tighten to the torque value specified for the disc-harrow assembly.