They are to adapt intakes with 2 15/16" single throat carb mounts to Stromberg 81, 48, 97 or Ford / Holley 94 dual throat carbs, all with the 3 bolt 2 5/8" bases.
You can also turn them upside down to reverse the adaption. 
Great intake adaptors for your Flathead Ford, inline Chevrolet 6, Chrysler 6, Dodge 6, Desoto 6, Plymouth 6, SCTA, Bonneville or El Mirage car, vintage race car, hot rod, street rod, rat rod, t-bucket or kool kustom.