Why do you think is necessary to screen these?

What use will these be?

kimmq is kimmsr

Al Tapla (the "inventor" of "gritty mix") and many other posters say it's important to sift out very small and very large particles from the "gritty mix" ingredients.

To do this, I wanted to know the sizes of the screen meshes to use.

(Some people give the sizes in millimeters (mm); others in inches; and others use general terms (such as "insect screen").

I have never made gritty mix so I can only talk about particle sizes here and make some educated guesses.

I'm going to guess 'very small' is under 1/8", maybe even smaller than that.

I noticed Turface MVP has detailed specs on its size range.

http://www.turface.com/sites/default/files/media/resource/turface_mvp_sheet_6-12-130.pdf

Only 11% of it is bigger than about 1/8" (6 mesh, 3.4 mm; 1/8" is 3.17 mm). So if you screened it with 1/8" which is the smallest one you listed, almost all of it would go through as 'fines'. About a fourth of it is less than 1/16" (20 mesh and lower) so if you wanted to screen out the fine end that may be the size to go for. But again I don't know what size range Al recommends either. Whatever you settle on here for the small end you probably want to run the granite through also, unless it is already clean of fines - i.e '1/4" clean' vs. '1/4" minus'.

As for 'very large', potting mixes I see have some pretty coarse stuff. I would think 1/2" or even chicken wire (3/4"-1"). Hard to know what your 'micro bark' looks like.

I think people are more conversant with gritty mix on the Container Gardening and Cacti/Succulents forums, so you might want to ask about it there.

I have posted my questions in the Container Gardening forum

http://forums2.gardenweb.com/discussions/4012484/potting-mix?n=6

but no one has answer them yet so I thought I'd ask them in the Soil, Compost & Mulch forum.

they really get us to do perfectly good work to obey these strange rules.

glib(5.5):

What are you trying to say? (The phrasing of your response makes it hard to understand)