The 100XR objective lens can replace any of the lenses in the lens cluster of the Sonlight Ultra microscope.
The Sonlight Ultra microscope comes equipped with a lens cluster that contains three objective lenses: 4X, 10X, and 40XR. In laymen's terms, that means each of the three lenses magnifies 40, 100, and 400 times what they're viewing. (The "R" means the lens is retractable to prevent scratching the lens or breaking slides.)
You can remove any of the lenses in the lens cluster by unscrewing it from its threaded socket. You can then add in its place an objective lens with a different magnification should you desire to do so.
That's why we sell the 100XR (1000x magnification) objective lens. Most serious students won't ever require such powerful magnification, but we offer it for those who really do need it or want it. (For further reading, see the article Do I need a 100XR objective lens?)
Note: The most common power for day-in and day-out high-powered viewing, even in a clinical laboratory environment, is 400x. The 100XR lens requires oil immersion of your specimen — and this process may result in broken lenses and slides. Requires immersion oil.