Hi,
Thanks for the second post, that's much clearer. In order to cut out that circle, you'd need to have two separate RailClone objects, as follows:
RC Object 1 - Creates the two top circles
RC Object 2 - Creates the bottom circle which uses a separate spline
You can then add the spline used in RC object 2 as a Clipping Spline in RC object 1 and change to mode to Exclude

I hope that helps
Paul