This series bearing roller model number for:BY,DC1,DC2,HY,HY-2,JZ,ZM,BK,DH1,DH4,HY-3,HY-4,HY-5,etc.. These same lot of bearing roller tolerance is less than from 0 to 0.015, and it made by steel GCr15 material, heated hardness HRC61~64°. bearing roller