This is not my design but a Remix of a simple design I had found somewhere, I cannot find the design now though.
My remix of this design thickens the book insert part as the original design was only a single layer and quite flimsy. I also extended the top part to make it easier to remove or turn to the page being marked.
I generally print it at .20 or .15 with PLA.
The author hasn't provided the model origin yet.