Designed for masonry flue application. Not suitable for metal chimney. Fits outside tile dimensions (inches): 10 x 14 to 12.5 x 16.25 24 gauge 100% stainless Steel hood with scalloped corners and roll-formed edges, 18 gauge 3/4 inch 100% stainless Steel expanded metal mesh Slotted hex-head stainless Steel mounting bolts for easy, durable installation Outside mounting provides greater free air space Expanded metal mesh turned inward at base allows cover to rest firmly on flue tile, closing any openings to protect against nuisance wildlife