These are mouse balls used in old PCs and workstations. Perfect for use in a Pythagoras Switch project. They are old, having been removed from old mice, so there may be some scratches/stains. Also, some with rubber surfaces may have undergone hydrolysis. Top row in the photo: Diameter: approx. 22mm, Weight: approx. 31g, 4 pieces, white rubber surface Bottom row in the photo: Diameter: approx. 25mm, Weight: approx. 66g, 2 pieces, metal surface Please note that it may take some time to ship.