These rubber grommets can be used on any case fans. They absorb the vibrations from the fan and reduce the overall noise level. You will need 4 of them per fan, one for each screw.
"They're little rubber grommet, they do what you want them to do :D
I found they fit more securely around M5 screws rather than the M4, however this doesn't negate their purpose. They're currently serving their purpose very well."