This .75in mesh 4in Round HY-C Liner Cap is constructed of 304-stainless steel. It is designed to securely clamp to the outside of both rigid and flexible stainless steel liners. It can also be used as a replacement cap on most double or triple wall chimneys. Includes removable mesh. Fits outside pipe dimensions from 3.5in up to 4.5in. The 6in round is pictured.