Structural bolts for steel connections are bought as assemblies – bolt, nut and washer – and their performance depends on all three parts and how they are installed. A purchase order that only says “Grade 8.8” or “A325” leaves out most of what matters.
Standards to Name on the Order
| System | Bolt | Nut | Washer |
|---|---|---|---|
| ASTM (inch) | ASTM F3125 Grade A325 or A490 (heavy hex structural bolts) | ASTM A563 (grade to suit the bolt) | ASTM F436 hardened washers |
| ISO / EN (metric) | EN 14399 system, property class 8.8 or 10.9 | Matching EN 14399 nut | Matching EN 14399 washer |
In the ASTM system, A325 and A490 are now grades within ASTM F3125. In Europe, high-strength preloadable structural assemblies are supplied to the EN 14399 series as matched sets.
What a Buyer Should Verify
- Markings: bolt head and nut markings show the grade and manufacturer’s identification required by the standard.
- Assembly compatibility: nut and washer grades are those specified for the bolt grade.
- Coating: plain, hot-dip galvanised or zinc-flake; galvanised nuts are tapped oversize, and some higher-strength grades have restrictions on galvanising.
- Lot traceability: bolts, nuts and washers supplied in identifiable lots, with certificates for each.
- Installation-related tests: where the project requires them, for example rotational-capacity testing of galvanised assemblies or pre-installation verification.
- Documents: certificates covering chemistry, mechanical properties and coating for each lot.
Store and Install as Supplied
Keep assemblies in their lots, protected from moisture and contamination, and do not mix lots on site. Lubrication and condition affect the preload achieved, so follow the project’s installation procedure and the relevant structural code.
Related: ASTM A325 structural bolts, ASTM A490 structural bolts and the fastener RFQ template.
Frequently Asked Questions
Are A325 and A490 still separate standards?
In the current ASTM system, A325 and A490 structural bolts are grades within ASTM F3125, used with ASTM A563 nuts and F436 washers.
Can structural bolts, nuts and washers come from different lots?
For traceability and consistent performance, assemblies are normally supplied and kept in identifiable lots with matching certificates. Follow your project specification.
Can all structural bolt grades be hot-dip galvanised?
No. Some higher-strength grades have restrictions on galvanising because of hydrogen embrittlement risk. Check the standard and specification before ordering a coating.
