1. Material and coating
Carbon steel, galvanized steel, A2/A4 stainless steel, brass, aluminium — the choice depends on the operating environment. For outdoor structures exposed to the open sky — hot-dip galvanizing (GOST 9.307) or A4 stainless steel. For dry indoor spaces, black or yellow passivated steel saves budget without sacrificing service life.
2. Property class
The bolt head carries a marking — 4.8, 5.6, 8.8, 10.9, 12.9.
The first digit × 100 is the tensile strength in MPa; the second reflects the ratio
of yield strength to tensile strength. For load-bearing connections — no lower than 8.8.
For dynamic loads — 10.9 and above.
3. GOST or DIN marking
GOST 7798, GOST 7805, GOST 7796 are different precision classes of bolts. DIN 933 (full thread) and DIN 931 (partial thread) are the European equivalents. Check against the design documentation: substituting DIN for GOST or vice versa may not pass technical supervision.
4. Compatibility with the structure’s material
Galvanic corrosion is a common cause of fastener failure. Aluminium and stainless steel get along; a zinc-plated fastener in a stainless structure forms a couple with an electrochemical potential difference. For mixed couples — an insulating washer or switching to the same material.
5. Documents and the batch
Request a quality passport and a certificate of conformity. The fastener batch records the steel heat, the production date, and the test results. For critical structures — selective incoming inspection for tensile strength and hardness.
Not sure about your selection? Send us the specification or drawing — a manager will select equivalents and check compatibility with your project.