"FMI Wood Fireplace Firestop Spacer for 12" Chimney Pipe. Only FMI Chimney Wood Fireplace Chimney Liners and Chimney Liner Accessories are approved for use with FMI Wood Fireplaces. They are UL approved and are not for use with any product other than FMI Wood Burning Fireplaces.Firestop Spacer for 12" Chimney Required at ceiling 19.5" x 19.5" Overall"Model: FS-10