BROSOL/SOLEX VELOCITY STACKSReplaces air cleaners to the carburetors for better performance and improved looks.Add 3% to 6% more airflow through the carburetorSold in pairsSlip-in spun aluminum stacks work with both 40mm and 44mm Brosol/Solex carburetors and kits (sold separately). 3-1/2" high x 4-1/2" outside diameter (2-3/4" outside diameter at base).