Bought these to replace the bearings in my Elecom Huge trackball mouse. I thought it was pretty nifty at first, but I bought the bearings and the mouse at the same time, so I might as well make a mod. Man, they make a world of difference. Let's see if they fit and use in my Logitech Marble trackball too. I can't comment on their exact size, but they fit my use case perfectly.