4" High x 3" High Collar
26 Gauge Galvanized Steel, Single Wall with No Insulation
Built with standard plaster ground flange all the way around the square portion.
Connects a 10" Round Duct to a 12" x 12" Diffuser or Register Vent.
The ceiling box is nailed into the attic rafters and plastered or dry walled around the flange called plaster ground.