I have 2 Silverston FM82's and one Silverstone FM121. So far, I have only tried the 121. When I want to screw it in, the screws are two thin and slip right out.
i dont think those fit. are you using the screws that came with the case or the fan? the fan, i would imagine...? anyway, you can always put a nut on the end of the screw, but im sure if you just go to a hardware store you can find some scres slightly larger than the ones you have.