5 mm Glass Column connection to all Packed TCD only, All other columns use P/N 221-10079-91 and Reducing Unions. Requires 2mm-to-n/n" Reducing Unions for Columns less than 5 mm Outside Diameter, 2 mm O.D x 1/16" O.D. Column Reducing Union = one 220-94669-01 (2mm x 1/8" = 220-90014-01,2mm x 1/4" = 220-90014-02)