Ball: Gcr15 Steel, heat treated, HRC56 min; Precision ground, polished hard chromium plated Body: Chromoly steel, heat treated, polished and hard chrome plated. Race: Nylon polymer with PTFE additive Sliding contact surfaces: Steel/NylonPhone: +86-592-580 8851 / +86-592-580 7618Email: sales@ldk-bearing.com ; benjamin@ldk-bearings.com