The Trend B63B bearing is designed for dust prevention and long lifespan, featuring a protective shield and being grease packed for life. With an outside diameter of 1/4 Inch (6.3 mm) and an inside diameter of 1/8 Inch. To ensure optimal performance and longevity, avoid cleaning with solvent or lubricating the bearing to prevent dissolving the grease. Always remember to scrape off any resin build-up and check the tightness of the fixing screw before using the cutter. Suitable for any eighth inch bore router cutter tasks.