i'm working on a weird robot and need to mount an arduino uno to it. my horizontal mount concept sucked big time, but this one is way better. The walls are 3mm thick, the bracket height is 25mm in total. The extrusion side holes are 5mm diameter. The standoffs are 5mm tall, and the holes in the standoffs are 3.2mm diameter, perfect for use with 3mm bolts. The standoff pattern matches the arduino uno. You may be able to use it with other variants of arduino-like boards. You may want to mount the bracket to the extrusion before you mount the arduino to the bracket.