brake block

plural brake blocks

1. on a bicycleOne of two small blocks fitted to a brake caliper, which rub on the wheel rim when the brake is applied.
2. rail transportA block fitted to locomotives or rolling stock, which rubs on the steel tyre of the wheel when the brake is applied.

   Braking is by non-metallic brake blocks throughout, two to each wheel.

   1960 February, “The first of London's new Piccadilly Line trains is delivered”, in Trains Illustrated, page 93

   1 more example

   There are two brake blocks per wheel of the locomotive, and each brake block is actuated by its own cylinder, which obviates rigging (except to the hand parking brake).

   1959 March, “The 2,500 h.p. electric locomotives for the Kent Coast electrification”, in Trains Illustrated, page 124

3. A block (perhaps wooden) used for braking a horse-drawn vehicle.