This is a 120mm fan cover, mostly common in computers. Like the million others out there, it protects the fans from foreign objects and your fingers from its blades. This design tho, also allows to swap grille colors and designs without unscrewing it plus when covering two or more fans together (as in computer radiators), it sprawls an overlapping design to make it seem like a seamless unit.

Designed in SolidWorks for Makers, this parametric design contains three configurations for single, double or triple and more fans, in double or more configurations, the screw tabs overlap the following frame and reduces mounting screws. The grille also “connects” to the next one enhancing the seamless design.

I created Fanswap as a way to mod my PC, what I wanted was not available and what I liked was way too expensive (CNC machined aluminum covers, anyone?), also the pain of changing the cover in a tight case, specially on radiators where the fan also comes off the same screws. Also, why did double and triple radiators never looked like a single cohesive unit?  

In the image above, the parts were printed in Overture black PLA and 3D Solutech Silver Metal PLA, I love this last one.

I have published the files for printing in Maker World and Printables.