Today I looked in the Audi parts fiche to make sure that ALL the A4 (1.8, 2.8, 96-00) filters were the same and they are. There are no different filters for 96-97 and 98-99. 

K&N has it listed as such in their catalog but it is WRONG. The only different filter listed in the Audi fiche is for late model cars, they have a "cold weather" filter; don't ask me. 

I'm a tech and have been installing the same filters in all A4s since day one. I just had to check the fiche and make sure before I posted this info. The ONLY correct filter is the 33-2125. If you install the 33-1675 in any A4, you WILL have a 1/4" gap bypassing air around the filter. 

• 33-2125 = 10" x 8 3/8"
• 33-1675 = 10" x 8 1/4"

If you have a 33-1675, I suggest you change it as a bypass around the filter is NOT a good idea.