I needed a couple of spanners to adjust the bed levelling screws on my Prusa Mendel. At first, I was going to download and print one, but then I decided to have a go at my very first real creation (from concept to physical print).
I measured the M3 nuts with my digital callipers (5.4 mm across flats / 2.3 mm thick), and designed a spanner with an open end at one end and a hex ring at the other, using Alibre Design PE(Personal Edition). I increased the gap by 0.5 mm (to allow for plastic shrinkage, and to allow the spanner to fit over the nuts easily), and exported an STL file. I then printed a pair.
They don't look too clean in the photo, but that is because my machine is brand new, and I am still learning how to optimise and calibrate it.
I am sure there are many other 3 mm Spanners you can download, but this is my own design, and I am proud of it!
I have uploaded the Alibre model file for those with Alibre PE who may want to modify the design; otherwise, just download the STL file.
Download STL file and print two (so you can hold both the bolt head and the nut). Use the ring end when you can, or use the open end when you need to.