sometimes screws aren't long enough, like when you have to attach a grill and a grommet/washer to the fan. using #8 machine screws and nuts will work in those situations where fan screws won't. on my fans i have a grill on one side attached with 4 fan screws, and it's attached to the case on the otherside, as well as a grommet and grill/filter, with 4 #8 1" machine screws and nuts. one thing i could do is just use a longer machine screw to attach the second grill on the other side, but i find it easier and convenient to have it "permantly" screwed in. you could find the machine screws at almost any hardware store. i got mine at home depot in packs of 6 machine screws and nuts for $.88.