Hart & Cooley 16 Series - 12" Round White Ceiling Diffuser (Fits a 12" Hole in the Ceiling) Designed to fit a 12" hole, overall diameter is 15-15/16" Step down diffuser rings deflect air stream 360 degrees Bright White finish Sold Separately: Butterfly Damper For This Diffuser (12" Hart & Cooley #12) All-steel construction