... ± 1 silk, absolutely guarantee the quality.2. Hardness: hardness in between 55 ~ 623. Imperfect rate: 100% through strict screening ... not exist visual visible crack, defects such as corrosion, used in home and abroad quality casters, bicycle, force of car ... automobile parts,slide bearing,caster wheels,computer peripheral products,toys,metal milling,hand tools and etc. G500 soft carbon steel ball made in ...