Preassembled High Back Rollout Shelf System for 12" Cabinet Openings. Featuring 21" Undermount Soft Closing Drawer Slides. Preassembled and ready to install mounts to bottom of cabinet. Soft closing undermount slides. 5/8" White Birch rollout drawer box with UV coating with1/4" bottoms. Overall Dimensions: 10 1/16" wide x 21 7/16" deep x 9" tall.