The 9688 was made as a Hyundai specific filter due to some issues back in the mid 2000's.
Part of it was the burst pressure is a little higher on the 9688, and there were issues with knocking that Hyundai blamed on the then recommended 7317/6607 filters.
The 3593a was initially a Honda specific filter that was redesigned at some point (hence the "a" at the end of the part number), but no idea what the redesign was.
I interchange the 9688 and 3593a on Hyundai/Kia vehicles (and on Honda motorcycles where they fit) with no concerns.
I think the new Champ made Supertech filters did away with the 3593a size and just say to use the 9688.
Part of it was the burst pressure is a little higher on the 9688, and there were issues with knocking that Hyundai blamed on the then recommended 7317/6607 filters.
The 3593a was initially a Honda specific filter that was redesigned at some point (hence the "a" at the end of the part number), but no idea what the redesign was.
I interchange the 9688 and 3593a on Hyundai/Kia vehicles (and on Honda motorcycles where they fit) with no concerns.
I think the new Champ made Supertech filters did away with the 3593a size and just say to use the 9688.