As a planet, Saturn has the highest flattening(ellipticity) which is 0.09796. So, it makes Saturn with the largest equatorial bulge as a planet and as such Saturn is the flattest planet.
However, I have encountered this statement from here:
Earth's Moon is even less elliptical, with a flattening of less than 1/825, while Jupiter is visibly oblate at about 1/15 and one of Saturn's triaxial moons, Telesto, is highly flattened, with f between 1/3 to 1/2 (meaning that the polar diameter is between 50% and 67% of the equatorial).
So, Telesto has a flattening value even higher than Saturn itself. I couldn't find any other body that has higher flattening value than Telesto. Does that mean Telesto has the highest recorded 'f' value?
Question: What celestial body inside the solar system has the highest recorded flattening value? Is it Telesto?
Note: Most of the asteroids, meteors, comets and small moons have irregular shapes and as such measuring the 'f' value is impossible and may have no useful value. I want to know which body has the highest recorded 'f' value.