Thanks for showing the pen and as only your 3rd pen it is very good and you could take it apart and remedy the diameters. I use bushes for guidance, but always measure the pen parts and the turned blank, even with the same kits there can be differences.
You will find lots of segmenters here, Jim is a leading proponent have a look at pens in the galleries. Have you done any segmenting or are you just starting to try it?
Peter