I thought the Stillen instructions listed "Fram filter PH3950, or similar". However, having said that, I am using K&N oil filter HP-1008. I've been using that since my first oil change (before installing the oil cooler) in place of the OEM filter. It seemed to fit the sandwich adapter fine, so I've been using the same since having the oil cooler on...running leak-free for 8000 km (5000 miles). So long as your filter surrounds the sandwich adapter opening it'll work...and of course, use the same procedure for changing an oil filter.