Solid of constant width

This object is a solid of constant width. If you print three of them and set a book on them, it is possible to move the book in any horizontal direction and the three solids will roll smoothly underneath it as if they were spherical balls. This shape is made by revolving a Reuleaux triangle about one of its axes.

I've also added a stand to display them on—in the shape of a Reuleaux triangle.