Pipe lengths provide the core part of the chimney system. Pipes should match the inside diameter of all other pieces and all pieces should be from the same manufacturer. The net length when installed is 1-5 8 shorter than the overall length of the pipe. Direct-Temp system features stainless steel inner and heavy duty galvanized steel outer walls. Heavy duty centering brackets keep inner pipe centered and chamfered edges allow for easy slide-together assembly. The free-floating inner liner allows the pipe to expand and contract under high temperature, without creating gaps or stress points. The LockTab(r) is a unique design that allows for 360° rotation while securely locking the sections of pipe together with just a push of the tab.Siliconozed fiberglass seal LockTab security Pipe rotates easily to align system components No sealant required High efficiency performanceFinish: Galvanized Fuel Type: Gas Inner Wall: 304 Stainless Steel Joint Connection Overlap: 1-5 8 Joint Connection Type: Twist-Lock standard on all diameters Length: 12-1 5 Material: Galvanized Steel, Stainless Steel Outer Wall: Heavy duty galvanized steel Pipe Class: Direct Vent Pipe Inside Diameter: 5 x 8 Pipe Shape: Round UL Listed: Yes Vent Construction: Double Wall