Simpson Duravent 9243N 8" Triple Wall Thimble This product requires: 2" air clearance to combustibles for all diameters Joint/Connection Overlap: 1-1/2" Joint/Connection Type: Twist-Lock standard on all diameters Outer Wall: .016" Thick Stainless Steel or .018" Thick Galvanized Steel Maximum Temperature Rating: Rated for continuous use at 1000, intermittent use at 2100