Spiral elbow features:The spiral eblow is a replacement for the solid weld seam elbow. It gives the same performance the solid ells give with the continious  * Airtight 4-ply lock seam construction * Meets SMACNA gauge requirements * Meets leakage Class 3 for 10" W.G. Duct construction class in a sample test section * Low friction loss * 45 and 90 degree 1.5 Centerline Elbows from 4" to 18" diameter 26 gauge galvanized construction * Labor savings - no sealant is required on the elbows other than where attached to the spiral duct