Yellowood Y2 Fingerboard wheels feature dual abec 7 bearings, a durometer of 60D for optimized grip/slide, and is 7.6mm in diameter. Dual bearings should be favored because they have more contact with the axle which makes them more stable; more stability means less wobbles and no jamming! These wheels are designed to fit perfectly with Yellowood Ytrucks. You could technically put them on Black River Trucks, but we do not recommend this as they may jam.