This mixing spring applies tension to the agitator mechanism inside the spreader hopper. It keeps the mixing shaft engaged with the fertilizer bed, preventing bridging and ensuring a steady flow of material to the metering disc. A spring that has lost its tension allows the agitator to slip, leading to uneven output and blockages at the outlet. The spring is wound to match the original assembly's free length and coil diameter, so it maintains the correct preload on the agitator arm without requiring shims or adjustments.