This disc is the marking disc for a seed drill or tillage implement. It cuts a visible furrow in the soil to indicate the edge of the previous pass, allowing the operator to align the next pass without overlap or gaps. The disc mounts on the marker arm and rotates as it contacts the ground; a worn or bent disc produces a shallow or inconsistent mark, which leads to uneven seed spacing at the headland. The manufacturer machines the disc to match the original hub geometry so the bearing bore and mounting bolt pattern align without shimming.