Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:5873189.

I created this design to divide the billy bookcase (Ikea) into 2 shelves.

This allows me to gain space for the books so I can put them in 2 rows, one low and one high and use the space under the shelf for other things.

It requires 2 aluminum rods of 5.5 or 6 mm.

It can be composed as desired, I recommend inserting a support at least every 2 full parts and half.