Intellimouse Trackball What Are The Rubber Rollers On Old Computer Mice Called?

What are the rubber rollers on old computer mice called? - intellimouse trackball

I'm a big girl of 10 years, Microsoft IntelliMouse Trackball I love you to death, but the rubber rollers under the ball is a little dry and rough, dirty and very much faster than striving in the past. Everything I need is to replace the little rubber tips and my trackball is like new.