1These steel balls are made of high quality Gcr15 bearing steel for pressure resistance and abrasion resistance 2Excellent surface quality, high hardness and high load bearing capacity 3Steel ball diameter is 6.35mm(1/4inch), and the tolerance is 0.002mm 4There are total 200 pieces in one set that you may use for many projects 5Mainly used for industrial products such as hardware tools, electrical appliances, casters, bearings, etc Features: These steel balls are made of high quality Gcr15 bearing steel for pressure resistance and abrasion resistance. Excellent surface quality, high hardness and high load bearing capacity. Steel ball diameter is 6.35mm(1/4inch), and the tolerance is 0.002mm. There are total 200 pieces in one set that you may use for many projects. Mainly used for industrial products such as hardware tools, electrical appliances, casters, bearings, etc. Specifications: Material: Bearing steel Gcr15 Diameter: 6.35mm(1/4") Grade: G10 Hardness: HRC65 Tolerance: 0.002mm Quantity: 200pcs Package Includes: 200 x Steel Balls