Summary

I recently came across the Open Source Optics collection by jpearce (it's really great, you should check it out: http://www.thingiverse.com/jpearce/collections/open-source-optics), and I came across the M3 hex thumb screw on there. It seemed to me that there was no way for this to be held in place, as these nuts are rounded, and also these have to be fitted before the screw is in place. I thought I could do better, so I have designed this press fit version, which should not spin.

EDIT
The original version had some bad things going on in the SketchUp file (some faces were missing/reversed). The new files should be fixed and printable now.

Instructions

This piece was made using SketchUp with the InvoluteGear plugin and the ExportSTL plugin.

I have left clearances at the outer rim of the nut and at the inner edges of the hex of 0.2 mm, which should be sufficient - but if not, these are easily altered from the SketchUp file using Offset and Push/Pull.