On the ring kit, the rotation radius is calculated to be 138.14 mm. This value has been used in at least one successful MaslowCNC high accuracy setup.
The rest of this topic explains how it was calculated:
I calculate the rotational radius of the ring kit to be ~139.82 mm +/- some very small amount…This is how I calculated it and would love someone to check my work. I based it off the drawings and the measurement @bar provided for the bearings in another thread (I assume the inner radius is 13 mm)
The premise is that the zero point is not the end of the first link, but rather the midpoint of the first link. Therefore, we need to calculate the distance from the center of the router bit to the midpoint of the first link. Furthermore, it’s assumed the cotter pin is very close to the same size of the gap between the chain link roller bearings and therefore the center of the cotter pin is practically at the zero point. The drawing below is not to scale.