SELKIRK CORP 208424 8-Inch  Support Box 8" inch, 8T-SB, Support Box Includes a black box for installation inside 16" O.C Contains joists, a cylindrical shield, support bucket, ceiling trim and four screws Intended for use when installing a model SSII chimney in an A-frame, a mobile home, or a ceiling under a narrow section of roof Made with the highest quality