Item: 1BZERBLKWD Zero Black Widow A-5 Bearings Single Set Zero bearings are sold in sets of eight, you need one set to create a complete. Bearings are critical to mount your wheels to the axle. We suggest keeping your bearings in good condition and clean to always have a smooth, fast ride. Bearings are sold in sets of 8, you need 2 bearings to mount each wheel to the axle (4 wheels x 2 bearings per wheel=8 bearings). Industry standard size is 608 with an 8 mm bore, a 22 mm outer diameter and a width of 7mm.