A bridge is usually a metal plate under which the pivots of the wheels and pinions turn. Both ends of the bridge are secured to the plate by screws. Generally the name of a bridge is associated to its function, e.g. centre-wheel bridge, barrel bridge, balance cock, etc.
A cock performs the same function as a bridge but is fixed only from one side.
Steady-pins, small pins fixed to bridges, cocks and springs to prevent them from turning.