Many 3D printers can print directly from an SD card instead of being hooked up to a computer all the time. This presents a problem of transporting SD cards without tying up your hands. Or pockets. A ring that you can put an SD card in is just the thing.
While a ring you can put an SD card in is a slightly silly solution, it's an excellent example of modeling based on physical objects. Both a finger and an SD card will need to be measured, and the design will have to be modeled too:
This chapter will walk you through the process of making a cool 3D-printed project, going through the following steps: