My GeeeTech Prusa i3 Aluminum printer came with a metal extruder bracket and I needed to make an adapter for the cooling fan. The extruder bracket had two existing M3 holes. This bracket utilizes the holes. I used M3 x 10mm screws and countersunk the holes so that the blower fan could mount flush. The holes for the fan are just pilot holes as I ended up tapping 6-32 threads into them.
I printed this with PLA at 200 Deg C on the nozzle and 60 Deg C on the bed. I used 100% infill and a 0.2mm height.