Its just a lil 4" fan inside of a 6"-4" reducer that i got at home depot for like 5 bucks. . .However the bottom, or intake, worked alot better for me. Its a 5"-4" reducer, but it fits the 4" fan perfect. I got the fan at Wal-Mart for $6.
Good Luck!!:weed:
Later. . .:joint: