Choosing an air cleaner comes down to three measurements. First, the carburettor neck: most Holley, Edelbrock, Carter and Rochester four barrel carbs use a 5-1/8 inch neck, while single barrel Strombergs on Holden sixes use 2-5/16 inch. Second, bonnet clearance: measure from the carb flange to the underside of the bonnet, remembering a drop base sits lower and a recessed base gains element height. Third, diameter: a 14 inch assembly flows more but needs room around rocker covers and boosters. Replacement elements are listed separately in paper, cotton and washable gauze, so you can service the assembly later without replacing the whole unit.