Been adding some sheetmetal to the blocks.
 
Check 'em out. CAD Blocks> Mechanical> Sheetmetal.
 
I always think of sheetmetal as duct "stuff." 

You might notice, I save all my drawings by default to AutoCAD 2000.
 
This is done at my various client requests. Not all have the latest 'n greatest AutoCAD programs, vertical or otherwise.
 
Been adding lots to MECHANICAL>SHEETMETAL directory.
Hope some use comes from the *.dwg's posted. All are 3D, FYI.

Need ductwork *.dwg files?
 
Let me know and I'll upload on request.
 
Sheetmetal is my thing.