I like conifer bark to improve drainage and reduce cost (around $2 per cubic foot for clean dry bark mulch). Then I screen it myself.
If it is held back even briefly by 1/2" mesh, I use it as top-dressing mulch outdoors (but I could grind it up if I wanted to).
Then from the rest, I remove dust and powder. If it passes too easily through 1/8" hardware cloth, it's too much like peat moss and kills the aeration & drainage. I use bark powder and fine fibers to lighten clay soil for filling raised beds (I mix it in well).
If it won't pass pretty easily through 1/4" mesh, it might be too coarse for seedlings or small pots, but be good as the coarse component for 5-gallon buckets.
In-between .1" and .2" seems right to me as the coarse component in potting soil, depending on pot size.
