The automobile brake drum is a brittle gray cast iron material:

The brake drum is a cast iron part shaped like a tambourine. It is fixed to the tire and rotates at the same speed. When braking, hydraulic pressure is used to push the brake shoes to contact the inner edge of the brake drum. The friction generated by the contact inhibits the rotation of the tire to achieve the purpose of braking. Drum brakes are composed of brake base plates, brake cylinders, brake shoes and other related connecting rods, springs, pins, and brake drums. Currently only commonly used on rear wheels. Drum brakes have lower cost and higher absolute braking force, and are mostly used in the rear wheels of small cars. However, its wear rate is higher, so the overall cost is higher at the same time.