📋 Bolt Grades Reference

Grade designation system

The two numbers of the property class code:

• 1st number × 100 = f_ub,min [MPa]
• 1st × 2nd × 10 = nominal f_yb [MPa]

ISO 898-1 specifies the actual minimum yield — for classes 4.8, 5.8, 10.9 and 12.9 it is slightly above the nominal value from the formula. The table lists the ISO minimums.

Selection & coatings

• 8.8 is the default structural grade (EC3); 10.9 for preloaded / HR bolts.
• Match the nut grade to the bolt (or higher).
• Avoid hot-dip galvanizing / electroplating on 12.9 — hydrogen-embrittlement risk.
• Proof stress f_pb is the preload reference: F_p = f_pb · A_s.