Amazon.co.jp: Miniature Bearings (Carbon Steel/4 x 7 x 2.5 mm/4 Pieces), Small Rotating Bearings, Ball Bearings, Deep Groove Ball Bearings, Small Bearings with Both Shields, Durable, High Strength, Low Noise, High Speed,
Amazon.co.jp: High Density Bearing Steel Ball 0.03 inch (1 mm) 0.3 inch (7 mm) 0.3 inch (9 mm) 0.4 inch (9.5 mm) 0.4 inch (1 mm) High Density Carbon Steel 0.4 inch (