Secure Temp 6″ Factory-Built Chimney 8″ Length Secure Temp’s 304 .016″ thick inner wall resists oil and coal corrosion better than the less expensive 430 stainless. The outer wall is .016″ thick 430 stainless. Couplers are .014″ thick and are made of 430 stainless steel. The floating flue, first designed by Security Chimneys, along with the double overlapped seam allows them to warranty their chimneys against chimney fires and corrosion, as well as workmanship and materials. Secure Temp has a 2″ clearance to combustibles. Features: Material: 304-alloy – .016″ inner wall, 430-alloy outer wall. Lifetime Warranty. Twist-lock installation. Approved for wood, coal, oil and category I gas. 2″ clearance to combustibles. UL Listed to 103HT, ULC S604, and ULC S610. Specifications: Overall Dimensions: 8″ (L) x 6″ (W).