Size Details: 1#: OD:20MM,ID:11MM,Ball Dia:5mm, 2#: OD:25MM,ID:12MM,Ball Dia:6mm, 3#: OD:29MM,ID:18MM,Ball Dia:6.35mm, 4#: OD:37MM,ID:29MM,Ball Dia:4mm, 5#: OD:40MM,ID:32MM,Ball Dia:4mm, 6#: OD:31MM,ID:22MM,Ball Dia:5mm, 7#: OD:38MM,ID:24MM,Ball Dia:8mm, 8#: OD:45MM,ID:31MM,Ball Dia:8mm, 9#: OD:34MM,ID:23MM,Ball Dia:6.35mm, 10#: OD:37MM,ID:27MM,Ball Dia:4mm 30-Piece, 10-Size Assortment – Covers all common bike bearing sizes (4mm-8mm / 1/6"-1/3") Hardened Steel Build – Durable, long-lasting, and built for heavy use Fixed Cage Design – No loose balls, fast & easy installation Fits All Bikes – Works with BMX, mountain, road, folding bikes & more Smooth, Low-Friction Performance – Restores ride quality and reduces maintenance DIY-Friendly – Perfect for beginner and pro mechanics alike