Simple modular parts tray in a 40mm grid. Designed with 0.2mm clearance between modules.
Horizontal grooves along outside allow you to slide modules into each other vertically and then you can lock them together with a wire/screw/thin dowel 2.8mm or thinner. (Alternatively, if you have Z wobble on your printer like I do, they can be jammed together and stay on their own. :P )
Internal corners rounded 5mm so you can still pick up small parts without the need for tweezers.
15x15x7.5mm compartments. (good for screws and small parts)
35x15x7.5mm compartments. (good for springs and small drill bits)
75x15x7.5mm compartments. (good for small hand tools)
155x15x7.5mm compartments in two parts. (good for hand tools and files)
123D Design file included so you can modify dimensions to suit your needs.