The tinman supply air duct plenum is a rectangular-shaped product made of galvanized steel with a 26 gauge thickness. It has a dimension of 21 x 14 x 23 1/2 inches and is compatible with various HVAC systems such as ducted evaporative cooler, packaged/rooftop furnace, and central air conditioner. It features both updraft and downdraft installation options and comes in a unit quantity of 20. This plenum is designed to connect the HVAC system to the ductwork and is a crucial component in ensuring proper air distribution throughout a building.