These are petri dishes that are about 10 inches square, made of clear sturdy plastic. Researchers use them once and throw them away – they cost $10 each new. The petri dishes are awesome for small pieces because they are thin so the parts inside don’t pile up / hide underneath each other. But you can see what’s in them from the top, side or bottom.
Several years ago, TLC asked for input from AFOL’s about what they thought was ideal for storage. I raved about these petri dishes, but I guess TLC had to make some compromises and created the multi-colored suitcase things that latch closed instead. My petri dishes have ridges which allow a small degree of interlocking when they stack, but they do not latch closed. Probably a poor design for kids.