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Apprentice Q&A · #011

How do I tell the difference between a Pittsburgh seam and a snap-lock seam?

1st YearDuct AssemblyYELLOW · Check First

Pittsburgh Seam: Features a deep, open pocket on one edge and a single raw flange on the opposing edge. Once inserted, the remaining flap of metal must be manually hammered flat down the entire seam length to lock it. Used heavily in high/medium-pressure commercial systems. * Snap-Lock Seam: Features a rolled female receptor pocket and a small barbed male edge. You simply push the male edge into the pocket until it audibly snaps together. It cannot be easily taken apart and is typically

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Plain-English answer

Pittsburgh Seam: Features a deep, open pocket on one edge and a single raw flange on the opposing edge. Once inserted, the remaining flap of metal must be manually hammered flat down the entire seam length to lock it. Used heavily in high/medium-pressure commercial systems. * Snap-Lock Seam: Features a rolled female receptor pocket and a small barbed male edge. You simply push the male edge into the pocket until it audibly snaps together. It cannot be easily taken apart and is typically used for low-pressure systems.

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Hey boss, I’m checking duct assembly: How do I tell the difference between a Pittsburgh seam and a snap-lock seam? I found the likely issue and want to verify the next step before I lock it in. Do you want me to adjust it now or check the drawing/detail first?

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Use this as training guidance. The foreman, approved drawings, project specs, manufacturer installation instructions, employer safety policy, and AHJ/code requirements always control the final answer.

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