Object of Constant Width - Tetrahedron

This is a shape which, like a ball, always has the same width all the way around. Though it appears to be a strange shape, you could run a board over it as smooth as marbles.

Here's a gif of these things in action: https://i.imgur.com/YpW7Cej.gifv

Inspired by the book "How Round is Your Circle" by John Bryant & Chris Sangwin.