Made this stopper because I like to have everything correctly aligned at the end of my shelves. I wanted something tall enough so I don't bother myself aligning it and it fits correctly anyways… I used cheap acrylic double side round tape to fix them easily (like a thick slime circle kinda)

Only found manga shelf that didn't fit my bookshelf as I wanted. I wanted my index finger height between top of the manga and the bottom of upper bookshelf. I also wanted a "snap-fit" edge (because I can't use glue) on the end to push my manga against so they are all aligned correctly. I had to make mine then.