Round bolt-on stainless steel chimney cover to prevent animals from entering or nesting in your chimney. Made from 100% stainless steel including the mounting bolts. 24 Gauge Single Piece Stainless Steel Hood with Roll Formed Edges. 16 Gauge Stainless Steel Base for Extra Strength. 18 Gauge 3/4" Expanded Stainless steel mesh. Model SS18U has a 18" inside diameter.