When choosing a box of a size to which a home delivery label can be affixed at the time of sending a small molded sample, a lot of cushioning materials had to be packed. If it is a thin box of this time, we are satisfied with a little cushioning material and enough label pasting area.
There are folds in 5 stages and one is used for the bottom so you can change the thickness by 15, 30, 45, 60 mm. (Inside dimensions -5 mm each) There is enough strength. Especially when using 30 mm thick it will slightly over if it is as it is, but if you cut off the overlapping part of the outer lid or paste the tape on the kitty eyes you can clear the delivery method of 3 cm limitation. I think that other sizes are equivalent specifications, but for reference