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A brake disc (rotor) is the metal disc that the brake pads clamp onto to slow the wheel.

When the pads press against the spinning disc, friction converts the vehicle's motion into heat, which the disc dissipates; commercial vehicle discs are large and heat-resistant for high loads and repeated braking.

Mounted at the wheel as part of a disc brake. Because braking is safety critical, discs and pads are inspected on schedule and replaced by axle set by a qualified technician.