mattress and spring Grade:55CrSi,60Si2Mn,65Mn Dia:6.0~16.0mm Standards: ASTM, BS, DIN, GB, JIS mattress and springGrade:55CrSi,60Si2Mn, ... BS, DIN, GB, JISAdvantage:1. Marerial: we select good quality spring steel wire rod.2. Surface treatment: advanced technology of shot ... rubbed smooth, almost can do zero defects for the surface.3. Quality assurance: Eddy current test online4.Service life: Ultra fine ...