Hi Toby, You can use radii larger than 30 with the color zone tool but you have to type in the larger number. The slider only goes to 30 (was originally created for x-ray structures). Making the slider range adapt to the size of the displayed data is on my Chimera requests page (item # 60, http://www.cgl.ucsf.edu/chimera/plans.html). I'm still not convinced that selecting connected pieces of a density map is going to be useful. If you choose a low threshold to get the structure you want plus some extra padding, then it ends up being connected to all kinds of other structures you do not want. It will only work if your structure is not connected to other structures and that is rare. I'm interested in hearing segmentation tool ideas but reluctant to spend time on it if it will not be useful. I'll be on vacation tomorrow until June 27. Other Chimera developers can answer your questions on the chimera-users list although I am the one who develops the volume features. Tom