This Bogen / Manfrotto Double Sliding Carriage with Single Brake is a rail lighting support system component.
Normally, the carriage with brake is mounted on the fixed rail so that it is locked into place, enabling the mobile rail to slide. If the carriage with the brake is mounted onto the mobile rail, you obtain the opposite effect, that is, the sliding of the mobile rail gets blocked, while the carriage can freely slide on the fixed rail.
