This is actually an imperial (standard/inch) bearing measuring 1/8 x 3/8 x 5/32 inch, with the equivalent metric measurements being approximately 3.17mm I.D. x 9.5mm O.D. x 4mm wide. This bearing is sometimes used in the Firepower 2800 series (300-450 size) motors that we sell.
Please check your motor for bearing size(s) before purchasing.