there is only 2 on that list with a base diameter of under 5". the ru5111 which i had but had to return because even though it is advertised as a 3" flange it actually has a 1/4 lip on the inside of the flange. when i called and asked why does my filter have this lip on it they told me it was so i would have a snug fit. well it was to "snug" cause my turbo flange has a small lip on it for a tight filter fit. the one lip would not pass over the other and the filter would only go on about 3/4 of an inch

they refunded my $$. the other filter i see on the list with a base diameter of 4.5" actually has a top diameter of 6". a reverse cone shape. not my style. uuugghh!