I looked at the BatchPCB FAQ and did not see the minimum width for silkscreen. For traces, yes. For silk, no. I’m guessing 8 mils. Does anyone know the real answer?
I have always assumed it is as small as you can go.
It is much less than 8mils, as it can easily do text in size 10 with a ratio of 8%. I estimate that this gives a line width of 1mil.
I imagine that you can go as small as you want, but after a point it it will just be too small to be shown.
Take a look at the Eagle reference board they sell, that gives a good idea of silkscreen sizes they BatchPCB does easily.
Thanks, gussy.