By definition, all of the outer vertices of the Platonic Solids lie upon a sphere.
Each of the 4 rings that makes up the TetraSphere touches 3 points of the face of a tetrahedron.
Also available as part of a Complete set of Platonic Spheres with nested Platonic Solids and
Without a Nested Tetrahedron
1.79 x 1.79 x 1.79 inches