12" DuraVent DuraTech Double-Wall Vertical Chimney Cap 12DT-VC1 This vertical chimney cap is required where pipe terminates above the roof line. It helps keep water and debris out of your chimney liner. Removable screws allow for cleaning of the chimney and spark arrestor screen. 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.