Final answer:
In a leading/trailing drum brake system, the primary and secondary shoe material is equal in size and usually interchangeable, distinguishing them from other brake parts like the anchor shoe, hold-down spring, or brake drum.
Step-by-step explanation:
In a leading/trailing drum brake system, the primary and secondary shoe material is equal in size and typically interchangeable. Unlike other components like the anchor shoe, hold-down spring, or brake drum, the primary and secondary shoes are designed to be symmetrical and can often be swapped without affecting the brake's performance. However, this is mostly the case with certain older or more basic drum brake designs. In modern drum brake systems, the primary and secondary shoes may still be different, with the primary shoe being the one towards the front of the vehicle and the secondary shoe towards the rear. It's important to note that while they may appear similar, the friction material and wear characteristics can differ to accommodate the dynamics of the braking system.