Part# AS0055P Aussie Speed stromberg Finned air filter assembly. This type has a boss in the centre of the lid so we can use one of our H bolts to hold the lid on.  These look great with the matching grey motor rocker cover & H bolts holding that on too.  The bottom diameter of the base is 2" 5/16' [58mm] ID and has two grub screws to grip the top of the carbi flange.