VXB.com offers a large selection of sizes, material, and grades of loose ball bearings. Here we have a 3mm Zirconium Oxide (ZrO2) loose bearing. Each loose bearing is graded according to its sphericity; the lower the number, the closer to being a perfect sphere. This featured bearing has a G25 grade in sphericity. Ceramic will never rust, making it ideal for any application with high humidity. Another benefit to full ceramic bearings is the minimal amount of fiction it produces.
Read more about this item at http://www.vxb.com/page/bearings/PROD/Kit7671