Torus and knotted tube

Spin a circle of radius r around an axis at distance R. While r < R the hole stays open; at r = R it pinches to a point (the horn torus); past it the surface passes through itself (the spindle torus). The second variant threads a tube along a trefoil knot.

((R + r cos v) cos u, (R + r cos v) sin u, r sin v)

On mathcurve.com as Tore