Fastener Strength Grades:Standard,Classification & Selec

[Abstract]:Strength grade defines fastener load capacity under ISO 898-1 and GB/T 3098.1 with X.Y marking system. X refers to tensile strength in 100MPa; Y equals yield-to-tensile ratio at 10% increment. For Grade 8.8, tensile strength hits 800MPa and yield stre

Strength grade defines fastener load capacity under ISO 898-1 and GB/T 3098.1 with X.Y marking system. X refers to tensile strength in 100MPa; Y equals yield-to-tensile ratio at 10% increment. For Grade 8.8, tensile strength hits 800MPa and yield strength 640MPa (800×0.8).

Grade Classification

Low Strength (4.6, 5.6)

Made of untreated low-carbon steel with low cost for non-critical lightweight assemblies including furniture fasteners.

Medium & High Strength (6.8, 8.8)

Quenched & tempered medium carbon/low alloy steel. Grade 8.8 is widely used for steel bridges and heavy machinery. Baosteel’s non-quenched 8.8 bolts debuted at 2025 Shanghai Fastener Show for NEV chassis assembly.

Ultra-High Strength (10.9, 12.9, 14.9)

Precision heat-treated Cr-Mo alloy steel. Grade 12.9 features 1200MPa tensile and 1080MPa yield strength for aerospace and nuclear applications; Baoji Titanium’s Grade 12.9 titanium bolts are mass-fitted on C919 aircraft flaps. Over-specification causes over 300% cost hike and adjacent component damage from excessive rigidity.

Selection Essentials

Custom surface finishes such as BASF nano-ceramic coating enable Grade 8.8 steady service up to 500℃ against high-temperature corrosion, while bare Grade 10.9 suffers sharp strength loss from erosion. Purchase certified parts with ISO/GB markings and factory inspection reports for tensile and hardness verification.