Bolts started in one corner only causing twisted flange

For TDC/Ductmate, the corner pieces help hold and locate the flange joint, but they are not what makes a crooked run acceptable. Get the duct sections level and aligned first, with gasket on one flange face only, then seat the corners and tighten evenly. A corner can look a little ugly and still work; a duct run that is twisted, racked, or out of level will keep fighting every joint after it.

Stop if

• Ask when connector type, gasket, cleat/bolt schedule, pressure class, or manufacturer detail is unclear.

Watch out

• Do not beat corners flat, force one corner tight while the rest of the duct is twisted, or use corner hardware to hide bad alignment. Do not call the joint done just because the corner pieces are installed.

Check

• Confirm gasket is on one flange face only and is continuous through the corners.
• Bring both duct sections level and aligned before starting corner hardware.
• Seat all four corners before final tightening.
• Check that the duct faces match, not just that the corner holes are close.
• Add required cleats/clips along the long spans. If no cleats are available, ask whether 5/16 self-tappers in the flange are approved for this shop/job.

Steps

• Align the duct sections square.
• Check flange faces, corners, gasket, and cleats/bolts.
• Fix damage or missing parts before tightening.
• Tighten or cleat evenly per project/manufacturer detail.
• Focus on the actual issue: bolts started in one corner only causing twisted flange.

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