Frag Rack and Protein Skimmer Adjustable Riser- 9x12 - Base-3.5-8 height-Reef Aquarium- Free 92 Pg PDF Ebook on Acrylic Filter Building 1/4" polished acrylic 9x12" Base Height is adjustable from 3.5 - 8" Nylon screws with wing nut for quick adjustment Perfect to raise your skimmer and for 30 Frags