8" DuraVent DuraTech 7/12 - 9/12 Trim Collar For Roof Support 8DT-RSTC9 This 7/12 - 9/12 DuraTech trim collar conceals the gap between chimney pipe and ceiling cut-out when used with a roof support. Approved for most fuel types 430-alloy stainless steel inner wall 2" clearance to combustibles ThermalTech blanket insulation eliminates hot spots Twist-lock connections for strong secure fits Able to vent large fireplaces and building heating appliances Clean smooth exterior finish 10â€-24†diameter pipes feature an .027†430 stainless steel inner wall and an outer wall of .029†galvalume or .027†430 stainless steel. A Refractory insulation is encased between walls. Only stainless pipes use the stainless end rings. Regular galvalume pipe uses galvalume end rings.