Telect's Global Seismic Frame duct capacity spacer (37398-xx) comes in 2.5" and 5.0" widths for 6ft, 7ft, and 2200mm high frames.  The 6ft spacers are P/N 37398-04 for the 2.5" wide spacer, and P/N 37398-03 for the 5.0" wide spacer.  The duct capacity spacer does not include the extension of the base guard like the duct capacity extenders do (P/N 0GS0xxSP-xx).  A drawing for the duct capacity spacer can be found below.