1、These bearings are made of high quality steel for low noise and long service life. 2、They are double shielded to avoid contaminants entering and save lubricant. 3、Bearings have a 15mm inner diameter, a 21mm outer diameter, and a 4mm thickness. 4、These are great for small hobby 15mm shaft/rod projects. 5、There comes total 10 pieces miniature bearings which you may use for many different projects. Features: These bearings are made of high quality steel for low noise and long service life. They are double shielded to avoid contaminants entering and save lubricant. Bearings have a 15mm inner diameter, a 21mm outer diameter, and a 4mm thickness. These are great for small hobby 15mm shaft/rod projects. There comes total 10 pieces miniature bearings which you may use for many different projects. Specification: Model: 6702ZZ Material: High-carbon chromium bearing steel Type: Deep-groove high-speed Rolling Element: Single row Inner Diameter: 15mm / 0.6in Outer Diameter: 21mm / 0.8in Thickness: 4mm / 0.2in Quantity: 10pcs Weight: 33g / 1.2oz(approx.) Package list: 10 * Bearings