Miniature Ball Bearing Bearing Industry Number 638 Bore Diameter 8 mm Closure Double Sealed For Environment Oily/Greasy Outer Ring Width 9 mm Outside Diameter 28 mm Ring Material Alloy Steel Seal Type Contact System of Measurement Metric ABEC Rating 1 Ball Material Alloy Steel Ball Material Grade AISI 52100 Bore Diameter Tolerance +0/-0.008 mm Cage Type Sealed Dynamic Radial Load Capacity 1 020 lbf Includes Retaining Ring No Lubricant Material Polyrex EM