This rechromed lid is found on many years and cars 1968 - 1971. The diameter of the lid is just over 17 3/4", fits on 17.84" air cleaner bases. Application Mercury Cougar Ford Mustang 302 and 351 engines without ram air. Ford / Mercury have had various part numbers listed for this basic lid over the years. The primary difference was the original lids included an engine size sticker. That is why there are so many listings, the basic part number is 9661. This lid was chromed in several applications, namely on the 1968 S code 390-4V or 390GT.