Are you compact? Stylish? 4U rackmount? Do you have nowhere to mount a 120mm fan? You might be an iStarUSA D-416.

These brackets use #6-32 nuts and #6x1/2 machine screws to mount a standard 120mm fan to the front of the 5.25 bays. You'll need 2 L and 2 R brackets.

There are two versions, the 25mm version should fit most fans, but ones with thick vibration pads may require the 26mm. Print with the rectangular side down. Removing the front door of the case is also recommended.

If you'd like to convert this to metric, I've included the f3d file.