This diffuser is designed specifically for the 4pin WOWLed magnetic 30cm RGB light strips that you can get from amazon they come in a three pack with a three way adaptor. 

If you print these with a translucent white filament they diffuse really well. I purposefully made these as simple as possible and they're designed to be printed with no supports, you may have to flip the model in your slicer as it's meant to be printed on it's back. The LED strips just snap in and have a solid hold you don't need to glue them in to the diffuser this allows you to reposition or disassemble as you need. 

I've included two files one 15cm and one 30cm this is in case you want to print on a mini and print two at once to make the 30cm you can't tell that there's a seam there at all when the lights are on if you line up the LEDs. For MK3s you will need to rotate 45 degrees in order to fit them on the bed.