This Spectre breather filter, also known as a crankcase vent filter, has a flange with an inside diameter of 10mm. By using the included adjustable worm gear clamp, this air filter will fit tubes with outside diameters from 3/8 inch to 1/2 inch (8-12mm). Spectre breathers use pre-dyed synthetic media for lasting color, feature a triple chrome-plated steel top and base, and come factory pre-oiled and ready to use. Note: Legal in California only for racing vehicles which may never be used, registered, or licensed for use upon a highway. See spectreperformance.com for CARB status on each part for a specific vehicle.