@John_Brock No longer always true.
In V7 a G2, non-circular arc blend option was added to FilletSrf. I had a discussion with @pascal about using “fillet” in Rhino for a non-circular arc blend. He said we can yell at him. Shrinking fillet surfaces - #14 by davidcockey
Back to FilletSrf in V7: The description of the command in Help has not been updated to include the option but it is shown in the Command line options. Rhinoceros Help
BlendType
CircularFillet
Creates a fillet surface with arc sections and tangent (G1) to the input surfaces.
G2Blend
Creates a blend surface connecting to the input surfaces with curvature (G2) continuity.
