6" 4/12 - 6/12 DuraVent DuraTech Trim Collar For Roof Support 6DT-RSTC6 This 4/12 - 6/12 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 10”-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.