the record's default variant, the RING cyclide: the ring torus R = 1, r = 0.45 inverted in the sphere of radius 1.6 about (1.9, 0, 0) -- all operator defaults. Inversion carries the torus's circular curvature lines to circles, which is the property that defines a Dupin cyclide
Sources
Chart reproduced numerically against the shipped implementation: fwd max 0.30 of tol, 0.0% of oracle beyond tol (tol floor 2.5 x 0.02719).
C. Dupin, Applications de geometrie et de mechanique (1822).
J. Schrott and B. Odehnal, 'Ortho-circles of Dupin cyclides', J. Geometry and Graphics 10 (2006).