Grade 10.9 structural bolts offer 1000 MPa tensile strength, widely used in structural steel and heavy machinery. Grade 12.9 — often supplied as hex flange bolts or tension-control bolts — provides 1220 MPa for critical high-stress joints.

Higher grades require careful attention to hydrogen embrittlement risks during plating and proper torque specifications during installation.

Always verify grade markings and obtain mill test certificates for safety-critical applications.