39mm Round Chrome Air Filters. Custom Clamp-on air filters are designed for racing motorcycles. The air filters allow considerably more air flow than a stock air box, however, carb adjustments will be required to get the proper amount of fuel to match the increased air flow. Generally a 25% increase in jet size can be expected. Requires 1 Pod air filter per Carb. Each filter is 3 1/4" in length. Sold Separately.