This design, based on the one shared by Taylor Stein on Youtube (https://www.youtube.com/watch?v=E0bhdr84FNU), is meant for Arduino Uno Rev1 and Rev2. It is also suitable for Rev3 although not all pin connectors become accessible.
Using M3 screws (26.2mm including head)

Geeetech i3 Pro B

No

Yes

0.2

30

I printed the model using a 0.3 nozzle:
First Layer Height: 0.3
Layer Height: 0.2
Layer Width: 0.51
Perimeters: 4 (I guess 3 perimeters could give better results)
Slicer: Slic3r 1.2.9