Lambro 622 Aluminum Pipe, 4" x 60"Smooth aluminum ducting snap lock. Major city building codes require that any dryer ducting. Drywalled wall must be a minimum of 5' to eliminate seams. Must be smooth in texture no ribbing. 4" x 60" Smooth aluminum ducting snap lock Major city building codes require that any dryer ducting Drywalled wall must be a minimum of 5' to eliminate seams Must be smooth in texture no ribbing.