This simple device has a long thin strip that slides into the gap in the spine of a bound notebook such as Moleskine or similar. A mechanical pencil can slide into the sheath outside the book. When the pencil slides into the sheath the pocket clip slides over the outside of the sheath. An opening on one side allows the pencil to slide down to the level of the top of the book so it doesn't stick out.

The holder sits flat on the table along with the book.

The model is designed to be printed on its side so the layers provide the best strength. None of the overhangs are more than 45º so no supports are needed.

This prints in less than 30 minutes using the default print profile for your filament. The examples in the photos were printed in Locyfens Glitter Shiny Silk PLA.