High strength bolts are essential components for steel structure connections. The grade marking represents mechanical performance, and 8.8 and 10.9 are two mainstream grades in global construction markets.
An 8.8 grade bolt has a minimum tensile strength of 800 MPa, while 10.9 grade reaches 1000 MPa. Higher grade means better tensile and yield strength. However, high strength bolts need strict torque control during installation. Too much torque may cause bolt fracture; insufficient torque will lead to loose connection under vibration.
High strength bolts are usually quenched and tempered. Surface options include black oxide, zinc plating and HDG. It is mandatory to match bolts with corresponding grade nuts. Mismatched fastener sets will cause premature failure of the whole connection joint.