HVAC.Sheet metal. Return air filter rack plenum,fit filter 20″x 20″x 4″

This is a 20″x20″x8″ Sheet Metal return air filter plenum.

There is a 3/4″ hem flange on one 20″x20″ end Outside the plenum (around the flange).
Dimensions 21-5/8″ x 21-5/8″ and height 8-1/8″, and the other side is fitted with an end cap.
From top to bottom the plenum is 8-1/8″ long .
There is a sliding door on the 20″ side.
The door can slide from ether side allowing for easy access.
Filter is 20″x20″x4′ ( MERV air filter 20″ x 20″ x 4″.
Actual size : 19 1/2″ x 19 1/2″ x 3 3/4″) not included .