MESH 316L SS #250, #300, #400, #500 ...

[Winblows]

What is the difference ?

 

[RichardV]

I know this is an old post, but I'll answer it anyway.
The numbers are mesh sizes. #250 is 250 openings per inch, #500 is 500 openings per inch. I used to use the #500 in my genesis tanks rolled up to make a wick.
For comparison window screens are usually #14 mesh and hardware cloth is usually #4 (1/4" squares) or #2 (1/2" squares) .