Nook’s precision bearing spacers with Arsenal 9’s bearing hard case bearings. Fast hard case bearing with a fell set of Nook’s precision spacers. Lock inn your wheel for better speed control in a turn. Fit’s all cast trucks. Make your cast trucks feel like a set of precision trucks. Bearing and spacer Size 10 mm X 8 mm Desecration of bearing and the difference, most soft case bearing have to much side to side play. Hard case bearing have better roll speed and a better bearing cage with less side to side play.