This gasket fits on either side of the insulator block. They are a direct fit for the 72 style insulators, but can also be used without modification on 70-71's as well (although they can be trimmed along the bottom to match the early insulators). Sold individually, 2 required per carb insulator block (4 per car).
If you are purchasing new insulator blocks, you will not need to purchase this gasket. It will work with any setup using 70-72 S.U. carbs.