Product Features Product Name: Steel Ball Material: GCR15 bearing steel Tolerance: 0.01mm Hardness: HRC60 Size (diameter): 15.081mm,15.5mm,15.875mm,16mm,16.5mm,16.669mm,17mm,17.463mm,17.5mm,18mm,18.256mm,18.5mm,19mm,19.05mm,19.5mm,19.844mm,20mm,20.5mm,20.638mm,21mm,21.431mm,22mm,22.225mm,22.5mm,22.8mm,23mm,23.5mm,23.813mm,24mm,24.5mm,24.606mm,25mm,25.2mm,25.3mm,25.4mm,25.5mm,26mm,26.2mm,26.5mm,27mm,27.5mm,28mm,28.57mm28.575mm,29mm,29.2mm,29.3mm,29.5mm,29.6mm,30mm1.high hardness, wear resistance, smooth surface, good roundness, not easy to rust2.These ball bearings are precision engineered for perfect consistency of weight, dimensions and finish.Made from high grade steel, these balls can withstand tremendous amounts of impact force.