Cold Plates - Solid Aluminum - 99.7% Pure Aluminum with 304 Stainless Steel product lines - Tilted and polished top surface to assure maximum cooling performance - Stainless Steel tub ing Fits Opening Size: 12" x 18" No. of Circuits: Four Circuit Len gth: 18' Tube I.D.: 5/16" Inlet & Outlet size: 1/