It is hard making tiny circuit boards.

OSHPark and most PCB fabs use a silkscreen process to apply text and graphics to boards. OSHPark tweeted it has a 5mil width limitation, in that it might not print line widths smaller than that. The standard seems to be 6mil. I use Diptrace's vector font which is a much tighter and in my eyes better font than Eagle or even Altium's (which seem the same). Through a bit of ignorance and luck I have found I can get simple text in this vector font down to 3mil width approximately through OSHPark. It only works for one or two characters (like numbers), can't be next to or partially on a trace to avoid ink runs. Anyway, I plan to revert to larger fonts as it is too problematic and we plan to start doing panels in the near future not through OSHPark. So I will be bumping up the thickness. In general I have had consistent text above 4.5mil. However, that may only work for OSHPark. DipTrace lets you specify line width/thickness as well as character width as a percentage of height. On a 3 point font, 40% may still be legible, and 50-60% don't look squished. So over the next few runs I will be improving the silkscreen text. To compensate, we will publish some annotated pictures in case the silkscreen is ruined on a batch.