This adapter is for Robo3D R1 Plus 3D printer. I use this adapter to replace the stock 25mm extruder fan with a very quiet fan. I tried several 25mm fan and found most of them poorly made. So I design this adapter so that it will fit 40mm fan. After replacing the fan, the temperature is stable.
Use the original screws to mount the adapter to the original screw holes. I use 15mm flat head screw and cap to mount the 40mm fan (the bottom two holes) and about 12mm wood screw to secure the top two holes.
Important YOU MUST ALSO REPLACE THE SCREW THAT SET THE X-MIN. IT NEEDS TO BE 10mm LONGER. This is important because the head is now thicker by 10mm on the left side.
Print the design upside down. Otherwise, the bottom won't stick. And print with support structure.
I also did two things to finally reduce the fan noise to acceptable level - replace the power supply and bottom plate fan. In case you are wondering how to reduce the total fan noise.