Apprentice question
Field check
Standard work. Do it right, keep moving.
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.