These fit Melissa and Doug tray toys, like the button shapes, pizza sutting, vegetable cutting, etc. since theirs don't come with lids, it's hard to stack them and keep pieces together. We also use them for organizing homeschool materials like math manipulatives, continent boxes, dry beans, and other Montessori activities. I love that the lid removes completely so they can function as a sensory bin. The inside base is perfectly flat too, no awkward ridges that make filling them difficult. These 6.2 Qt boxes fit PERFECTLY in the Ikea Expedit (or new Kallax) square shelving system. You can stack 4 together in one space, totally maximizing the shelving unit capacity! I'm super bummed they don't offer this product on line though, I need a bunch more and the store usually only has a handful available at a time. Similar size to a product that the container store offers, but these are a lot less expensive. I've used them now for 3 years and not one shows wear, and keep in mind, we use them for kid's toys, so they do see a lot of action!