An out-of-square duct section fights every connection on all four sides. Identify how far out of square it is before installing - forcing it in creates gaps, stress, and bad seals at the joints.
Do not force an out-of-square section into a run and try to make the joints work around it.
Check
Measure diagonals: measure corner to corner both ways. If the two diagonal measurements match, the section is square. If they do not, the difference between them is the out-of-square amount.
A small amount of rack may be correctable before the section is hung, depending on the piece and shop standard. Do not guess if the section is noticeably twisted.
Significant out-of-square usually means the section needs to go back to the shop or be remade. A badly racked section will gap at the joints, fight the drive installation, and leave the run out of alignment.
Do not install a noticeably out-of-square section and try to force it to fit - you will transfer the rack into the run and stress every adjacent joint.
Mark the section and set it aside before it gets used by mistake.
Steps
Measure diagonals: measure corner to corner both ways. If the two diagonal measurements match, the section is square. If they do not, the difference between them is the out-of-square amount.
A small amount of rack may be correctable before the section is hung, depending on the piece and shop standard. Do not guess if the section is noticeably twisted.
Significant out-of-square usually means the section needs to go back to the shop or be remade. A badly racked section will gap at the joints, fight the drive installation, and leave the run out of alignment.
Do not install a noticeably out-of-square section and try to force it to fit - you will transfer the rack into the run and stress every adjacent joint.
Mark the section and set it aside before it gets used by mistake.
Say this to your foreman
This section measures [X] on one diagonal and [Y] on the other - it is out of square by about . Do you want me to try to rack it back, or should it go back to the shop?