Edit: Thanks for the feedback: Updated to v2 with a better latch flattened the edges so it sticks better. There is only so much you can do with a 3mm section though.

This is a simple binder ring with a more secure connector.

Instructions:

1. Print it out
2. separate the opening carefully (used a xacto to pry it open)

I printed with 0.2mm layers using PLA+ for strength