HY-C 184B Duro Shield Single Flue Aluminum Band-Around Brick Chimney Cap, 21" x 21" Made from maintenance free non-corrosive Aluminum Fits outside brick dimensions 20.5 x 20.5 - 22.5 x 22.5 Hood is made from 18 gauge diamond embossed Aluminum Mesh is 16 gauge Aluminum expanded metal Lid size: 23.5 inch x 23.5 inch