I love countspatula's tray design where you can pour the parts back into a baggie or storage container. I have printed several and use them all the time. I always wished they were stackable. So I made a version that was stackable.
This part is also optimized for 0.4 mm print nozzles. The walls are an integer multiple of 0.4 mm and print exactly with 2 shells. These optimizations cut printing time in half!
The base is designed to print at 0.28 mm layer height (instead of 0.3 mm). Many 3D printer motors have a 0.04 mm z-axis stepper resolution. They can move to other positions, but the motor is holding between steps and is not stable. When using an integer multiple of 0.04 mm for z-axis layer height, the layers are much cleaner and have better layer-to-layer adhesion.
You can watch timelapse videos here: https://youtu.be/nWBk2_kmrwQ https://youtu.be/lXnrs0QPYfQ
UPDATE: 9/11/2017 Added a 50 mm x 50 mm tray in addition to the standard 50 mm x 100 mm tray.
UPDATE: 9/15/2017 Added a 50 mm circular tray.
Monoprice Maker Select V2.1
Use 3 top and bottom layers. The only thing with infill is the small lip for stacking