Bring the flange together evenly: not leaving room to get tools on flange bolts. Start hardware in a balanced way and do not twist the flange or crush the gasket.
In Rectangular Duct Assembly: TDC / Ductmate / Flanges, I’m looking at: What do I do when not leaving room to get tools on flange bolts? What should I verify before I cut, drill, seal, cover, move, or install?
Do not
Do not install flanged duct where no one can tighten or inspect the joint without approval.