I've seen lots of ideas for paintbrush holders, on here and elsewhere, and liked a lot of them, but they were all beyond me in one way or another.
I'm visually impaired, and one of my problems is reading the size number that's stamped on the brush - even if the paint hasn't worn off in use. And I have to do this every time I want to change brushes. [As you can see from the photo, I even tried writing in marker pen on the brushes, but that only worked for the bigger ones, and not very well even then.]
I eventually decided to revive something I'd done years before - definitely not elegant, but it works for both storage and ID.
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Step 1: Needed:
 block of polystyrene
 duct or parcel tape
 tool for making small holes
 tool for enlarging the hole [I used crosscut screwdriver]
 knife for cutting tape
 marker pen
Step 2: How-to
1 - wrap the polystyrene block in tape - this protects it and prevents it from flaking or breaking.
2 - poke small holes with the small tool, in rows and columns, number depending on how many brushes you have or are likely to have later.
3 - use the larger tool to make the holes bigger.
4 - put your brushes in size order in the holes.
5 - write the sizes on the front of the block for easy ID
Your labelling will probably be a lot smaller, but I need the numbers this big.
And there you have it. Brushes all neatly [ish] sorted by size, and each size clearly [ish] marked.
Late afterthought: I'm sure that corrugated cardboard would work just as well; enough layers to make a block, taped all over and punctured as above.