M12*40 Carbon Steel Black High-Strength Bolts

Grade 8.8 carbon steel construction achieves a minimum 800 MPa tensile strength, meeting the requirements for general steel structure connections under GB/T 5782 and DIN 931 standards. The black oxide surface treatment provides adequate corrosion protection for indoor or sheltered steel structures, while the matte black finish reduces visual contrast in painted structural assemblies.
For higher-load applications such as primary structural nodes, high-rise steel frames, and bridge connections, 10.9 grade options (compliant with GB/T 1228) are available. Surface finishes extend to Zinc, HDG, Phosphate, PTFE, and Dacromet to suit different environmental exposure categories.
Manufactured to GB/T 9125, ISO 7411, DIN 6914, DIN EN 14399, and ASME B18.2.1. Compatible with standard heavy hexagon nuts (Grade 8 or Grade 10) and large flat washers. OEM/ODM customization supported for non-standard lengths and specifications.