They're called
Solids of Revolution in some places. Designed through some high falutin math that Monster could probably explain, these obese pyramids are of constant width. No, they don't look it but they are, in every direction, no matter how you measure them.
I was given several sets last Christmas. Mine are some sort of molded phenolic I guess, two sets about one inch(2.5cm) high, and several sets about 3/8 of an inch(.95cm). I'm arbitrarily calling three a set, as that's the minimum to do this demonstration.
It's eerie to watch, but with your hand on the book it's absolutely smooth as ball bearings.
This is the label on the bag.