This brake disc is the friction component in the service brake assembly of the host tractor. It is splined to the axle shaft and rotates with it; the stationary caliper pistons clamp the disc to generate stopping torque. The disc is machined to match the original spline profile and thickness, which ensures the caliper pistons travel within their design range and the parking brake mechanism engages at the correct stroke. A worn disc reduces clamping force and increases pedal travel before brake engagement. When replacing, inspect the mating friction surfaces on the caliper pads and replace them if glazed or uneven.