This sleeve is meant to slide over the focus ring on the Fuji X100 and X100S. It gives you a larger surface to grip when you are adjusting the manual focus of the camera.
There is also an alternate model that includes a Leica style focus tab which helps in quickly fine tuning a manual focus. For that part, go here: https://www.shapeways.com/model/1382490/fuji-x100-focus-ring-sleeve-with-focus-tab.html?li=my-models&materialId=25
NOTE: Due to variability in the finishing process, a small piece of tape may be required on the inside of the ring to ensure a tight fit.