The drawer extensions are lightweight spruce and allow you to increase the volume of your existing galley drawers by mounting to the top edges and fastening firmly to the existing drawers. Notches are cut out of the back of the top and middle drawers to account for the latching plates and sink plumbing.
 
For some additional insights into the drawer extensions and how to install them, please see these youtube reviews by MULTIPLESHOTSFIRED and Brian Whidden.