Even a 50-micron gap is only a gap in a barrier, and most of those spores will remain inside or outside of that barrier, caught on the solid sections...
If 1/100th of the total gets in or out of that mask, you can still get sick, but you've kept 99% of them out, and that's probably enough to keep you safe...
There's more gap than barrier. Here's a modified version of a portion of
one of my microscopic pictures of an N95 mask, that I took about a month ago…
View attachment 356616
I scaled it up to that each pixel represents a 0.2-micron square, which represents the upper range of the size of the #CoronaHoax2020 virus. Inside that red circle, I've colored one pixel red, to show how small the very largest #CoronaHoax virus is, compared to the scale of the picture as a whole. You probably cannot even see it on this picture, without loading it into an external viewer and zooming in. Here's an enlarged version of just a small portion of the above image, so that you can see the pixel (now, scaled up to 4×4 pixels…
View attachment 356617
It's mostly empty space,between the fibers that make up the material of the mask.
Something bigger than the gaps between the fibers, obviously, won't get through. Something that is smaller than those gaps, but a significant portion of that size, probably stands a good chance of being stopped. Something as tiny as a virus—something as tiny as that pixel—certainly does not have a 99% chance of being stopped. Probably not even a 10% chance of being stopped. Possibly not even a 1% chance of being stopped.