These have a very specific size but don't come with a key for some reason. Here is one.
I am very much an enthusiastic amateur when it comes to designing. My designs tend to have two things in common
1) They serve a purpose. I like to design functional objects which have a real-world use. 3D printing for art is fine, but it's its real-world application which will take the technology forward
2) Wherever possible I design to be easy to print and try to eschew supports or complex printing; modifying the design where necessary and possible to achieve this.