This is for a brand new set of adjustable metering blocks.  These fully adjustable metering blocks allow you to maintain control of your carburetors fuel delivery.  They feature improved response over stock and are fully tunable for both street and race applications.  They retain vacuum passage for distributor vacuum advance.  These are a direct replacement for Holley - they fit all 4150 and 4160 style carbs with 582 jets.  This is for the pair of blocks.