2 mm is not very big as stones gone but can still raise hell in the ureter or urethra. Sometimes they will further break up and become almost like sand which would pass through the trap.
The time I had them for 12 days, I kept passing tiny ones about the size of a coarse grain of sand or even smaller.
The filter did catch them tho. It was very fine. I would of course rinse the trap each time but not backwards so the tiny bits stayed. At the end of the 12 days there was maybe a dozen tiny ones still trapped in that mesh.