The idea behind this project was to find a way to crate some notebooks for my students.

1. O-ring: I began with the simple O-rings in the design. They worked well but to hold the papers but allowed too much vertical play between the rings for my liking.
2. O-ring-curved-blade: I decided to try and design a blade that would pass through the O-rings both to close off the loop and vertically stabilize the rings. I created a curved blade but found it difficult to print long sections with the curved blade.
3. O-ring-straight-blade: I attempted to make a straight blade that would run through the back interior the the O-ring. It was functional but I didn't love the look of it and worried that it might not be strong enough.
4. D-ring: I came across the D-ring created by edjwing (https://www.thingiverse.com/thing:4310679). I modified and enlarged the shape and included a slot through the flat side of the D-ring. So far, I am most happy with this design.

I hope others can learn from this, and will continue to build up from and improve the design.