This brake disc is the rotating friction component in the service-brake system of the host tractor. It is mounted on the axle shaft and is clamped between stationary friction pads when the brake pedal is applied. The disc's friction faces convert kinetic energy into heat to slow or stop the vehicle. Over time, the friction surfaces wear and the disc thickness decreases, which increases pedal travel and reduces braking force. The disc's thickness and surface finish match the original assembly's specification, so the caliper's clamping force and pad clearance remain within design limits. On replacement, inspect the axle hub for runout and torque the wheel bolts to the manufacturer's specification.