This brake disc is the friction component that slows the tractor's drive wheels when hydraulic pressure clamps it between the stationary and rotating halves of the brake pack. It sits inside the axle-mounted brake housing, where its contact surfaces transfer braking torque to the hub. As the disc wears, the effective clamp force decreases, leading to longer stopping distances and potential overheating of the remaining friction material. The manufacturer machines this disc to the same thickness tolerance as the original assembly, so no shimming is required during replacement. On reinstall, clean the hub pilot and torque the retaining bolts to specification.