Our spiral pipe combines for you the economies of light gauge metal with our spiral lock-seam construction that guarantees maximum rigidity and strength, the duct work requires fewer joints and hangers. All spiral spiral pipe measures the even inch inside for example: a 6" diameter pipe is 6" I.D. Standard length from our stock is 10', however, 5' lengths can be ordered for an additional cut charge of $10 per section. We also have pipe in diameters larger than 24", please call for pricing. Quick-Lock pipe is also available. Please see the above link.