The K&N Stubstack is designed to increase the airflow of carburetors by decreasing the restriction around the choke horn. The Stubstack fits inside the air cleaner housing and slides snugly down over the choke horn. This K&N Stubstack fits the majority of Holley 2300 Series carburetors. The Stubstack is designed to fit 2 barrel popular models within this series. Holley carburetor list numbers are stamped on the choke horn.