Yeah, I'm a huge fan of those soft silicone studs when using cheaper fans that aren't likely to be precisely balanced. Zip ties also works, provided they're not too tight.
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As far as I'm concerned, rubber corner bumpers are cosmetic gimmicks that can f*ck off. The reasoning behind them is dumb as hell because what is the point of a vibration-damping bumper if you're going to create a completely rigid mechanical lock between the fan frame and the case by screwing a metal screw directly into the hard plastic frame?! All the rubber pad is doing at that point is getting in the way!
The only situation where they have any merit whatsoever (and IMO they're still far too thin and firm to really offer significant benefit) is when you have a tower cooler that presses the fan frame directly against the heatsink fins using LOOSE wire clips. If the clips are too strong, they compress the rubber and prevent the deformation that is supposed to absorb vibrations. If the clips are too strong, they're likely also stiff enough to transmit fan-frame vibrations to the heatsink themselves,
Use the rubber studs as pictured because you can buy them in bulk for $5. They are the only things that actually ISOLATE the case fan from the frame with a flexible, vibration damping material. Regardless of whether your fan has rubber bumpers or not, If you are using metal screws you are basically guaranteeing that the unstoppable force (wobbly case fan) is
directly interfacing with the immovable object (steel of the chassis).