Multi-media shelf is designed to transform your rock n roller cart into a fully functional mobile workstation. the lamain shelf measures 24" x 36" to provide ample work space for mobile sound, film production, testing equipment, and other professional on-site applications. the upper shelf can hold up to 50 lbs, and measures 10" x 36", allowing additional equipment to be set above the main workspace. the combined cart shelves can handle a total load of up to 200 lbs. the cart shelves are covered in a heavy duty carpet for durability, and fold for easy storage and transport. The Multi-Media shelf fits models R8, R10, R12 model# RSHM2 Not sure which cart model you have? Click here... For more information on the functionality of the shelf, please see the excellent blog from Film Sound Pro Fred Ginsberg. Additional resources can be found on Fred's Rock N Roller page.