This is a combination lock container with 1000 possible combinations. Inside is a space large enough to fit a key, some money, or whatever you feel like hiding away. The top of the container has an eyelet for attaching a keychain, and also makes it easy to open once the combination has been entered.
In the project files there are files for #0 - #9, pick the three digits that you would like to be in your combination and print those out. The order you put them on when you assemble it determines the order of the code.
A note - obviously a 3D printed lock such as this one could be forced open by breaking, this is nonetheless still a very neat object to print.
The only part that needs support material is part "L2", I had success using the 'Pillars' option in Slic3r.
Once you have the parts printed, assemble the number rings on the main body. Make sure that you have the numbers facing up, and have them in the correct order for your code. The top cap can then be carefully glued on, making sure not to accidently bond any other parts together.
This was designed in Autodesk Inventor 2016 and AutoCAD 2015.