I don't know how you could tell the size looking at pictures, since they are shot at an oblique angle. Well, the 1/20" had one straight on, but it's so washed out you can't see the mesh. Then there is the whole issue of scale/zoom on the photograph vs. a photo from anywhere else.

I'd be tempted to take them at their word that if the mesh size is given as 1/8", the holes are 1/8" x 1/8", but if it's that critical I can understand your wanting to confirm it. I happen to have a digital micrometer so it would be easy for someone like me to check it, but everyone doesn't have that available.

The bottom of the item page on Amazon, under Videos, has one that says SE Sona Enterprises. A google of that name comes up with a company in California.

https://sonasiya.com/index.php?main_page=page&id=17

@toxcrusadr I am comparing sifters that I actually own, not looking at photos.

Having purchased and fabricated sifters from multiple vendors, I would disagree that you should take anyone at their word. The problem with small openings is you have to account for wire width. A "1/20" of an inch sifter is often a 20 x 20 grid in a one square inch area, and some vendors reliably reduce the size of the reported openings by the wire size, whereas others just report on the theoretical value based on a zero-width wire. Sometimes the figure they are reporting is accurate and they have already removed the wires in calculating the opening. Sometimes that is not the case. Until you ask the manufacturer you do not know.

How would a digital micrometer be accurate for this? At 1/30th of an inch, you would need magnifiers just to see the pattern, and holding a digital micrometer in alignment would be tricky at best. You would need some kind of micrometer on a tripod and the ability to shift the pan underneath in incredibly small increments, all while observing the alignment under magnification.

I think you located the company and thanks!

@toxcrusadr Your idea of blowing up a ruler and counting spaces is a very good idea. I am sure that would give you a fairly accurate estimate.

Here is a table produced by a maker of custom sifters, and it shows the difference between the theoretical maximum opening size and the nominal "real" value. Here is how to read this table:

1) The first column "Micron" represents the theoretical maximum value if the wire width is zero.

2) The "Nominal Micron" column is what you actually get when you take out the wire width.

3) The "Wires/Mesh" column tells you the number of openings created in a one square inch space. For the 1/2" mesh at the very bottom, a 2x2 matrix would give four openings in one square inch.

As the opening gets smaller, the effect of the wire width becomes much more significant.

Interesting. I used to work in a lab analyzing rocks, and of course step one was to crush up the rock and sift it through standard mesh sieves. We'd just use the sieve number - "100 mesh" for example - as required by the method. I never thought about how complicated this was.

It appears that the openings are actually rectangular for all but the largest sizes. For example "100 micron" has 30x150 openings in a square inch. That would mean the holes are 5x as long as they are wide? Assuming the wire was the same size going both directions that is.

@toxcrusadr Good catch on the rectangularity of the openings at some sizes. That surely does affect what filters through, comparing against a square opening.

I think if you wanted to really get a precision opening, you would probably want to use a perforated sheet of stainless steel, where each opening could be a precision-drilled circle. Those types of sifters are stronger as well, but they are pricier too.