This image shows a 2RU Under Bridge Rack. It is also available in 3RU and 4RU. The Under Bridge Rack attaches to the underside of the shelf.
It is particularly useful when clear unobstructed shelf space is required on top of the bridge shelf, for example when multiple monitors are being used.
It utilizes slots in the rear of the M Rack Extrusion for a strong metal to metal suspended connection.