Description: -These ceramic bearing balls have extreme rotation, perfect for applications where premium performance bearing balls are required to meet your needs. - Lighter and stronger than tungsten carbide, these silicon nitride balls are diamond polished and guaranteed not to shatter or melt in the most extreme conditions. - Higher hardness than chrome steel balls. Vickers hardness up to 1700HV - Especially useful for bicycles, casters, drawer slides, door locks and many other applications. For a variety of purposes, list some of the most common things below. -9.8 mm is often used in clusters and older English-style headsets -6.35 mm is often used on rear wheel and bottom brackets -4.7 mm is commonly used on front wheel -3.9 mm is commonly used for headset with push cups Specifications: Size: 2 mm Tolerance: +/- 0.015 mm Material: Brass (H62) Package Content: 200 pcs