Chim-A-Lator 321818 18" x 18" Black Galvanized Steel California Chimney Cap with 5/8 mesh is the perfect way to help a chimney function at a optimum level. This Chimney Cap keeps out all of the debris and protects the chimney from any disruptive weather conditions. The width measures from 16” to 18.25” and the length measures from 16” to 18.25”.