Steel structures rely on thousands of bolts to transfer loads safely between beams, columns, braces, and plates. When the wrong bolts are selected, small details such as property class, coating, or nut–washer combination can lead to connection problems, rework, or even serious safety risks. For overseas buyers, engineers, and distributors, understanding how to select steel structure bolts is a key part of every project.
This article explains the main standards, materials, and design factors behind steel structure bolts, with a focus on requirements common in Australia, New Zealand, the Pacific, and other international markets. It also covers practical procurement checklists and inspection points so you can communicate clearly with your suppliers and installation teams.
Whether you are purchasing high-strength bolt assemblies to AS/NZS 1252, structural bolts according to ASTM F3125 Grade A325, or general structural fasteners based on ISO 898-1 property classes, the principles in this guide will help you choose suitable bolts and discuss the details with confidence.
1. Why Bolt Selection Matters in Steel Structures
In a steel structure, bolts are part of the designed load path. They must work together with beams, columns, gusset plates, and base plates to transfer loads safely. Good bolt selection helps you to:
- Achieve the required shear, tension, or combined capacity of the connection
- Control slip between plates in friction-type joints
- Maintain clamping force over time, even under vibration or temperature changes
- Provide adequate corrosion protection in the actual environment
- Simplify installation, inspection, and maintenance on site
Typical uses for steel structure bolts include:
- Column–beam and beam–beam splices
- Bracing connections and gusset plates
- Base plates and anchor systems (often combined with concrete fasteners)
- Purlins, secondary steel, and accessory steelwork
- Bridges, towers, industrial sheds, warehouses, and multi-storey buildings
One project may use several bolt grades, sizes, and coatings. For example, internal dry areas might use black 8.8 bolts, while external coastal zones require hot-dip galvanised high-strength assemblies to AS/NZS 1252 together with appropriate galvanizing requirements such as AS/NZS 1214. Clearly separating these requirements in RFQs and purchase orders is essential.
2. Key Standards for Steel Structure Bolts
2.1 ISO 898-1 property classes
ISO 898-1 defines the mechanical properties of carbon steel and alloy steel bolts, screws, and studs, including minimum tensile strength, proof load, and yield strength. You can find the standard overview here:
https://www.iso.org/standard/42281.html
For structural steelwork, the most common property classes are:
- 8.8 – typical high-tensile structural bolt for general applications
- 10.9 – higher strength for compact or heavily loaded joints
- 4.6 / 5.6 – lower strength, more common in non-critical or secondary structures
When you specify “M20 × 80, property class 8.8, ISO 898-1”, you are defining the required mechanical performance of the bolt. The actual geometry (head type, thread length, shank) must still follow a dimensional standard and the connection design.
2.2 AS/NZS 1252 structural bolt assemblies
For projects in Australia and New Zealand, structural bolts are usually specified according to AS/NZS 1252, which covers high-strength steel fastener assemblies for structural engineering, including bolts, nuts, and washers. The standard is divided into:
- AS/NZS 1252.1 – Technical requirements
- AS/NZS 1252.2 – Verification testing of bolt assemblies
These assemblies typically use property class 8.8 or 10.9 bolts, matching nuts, and structural washers. Hot-dip galvanised assemblies must meet additional coating requirements, often referring to AS/NZS 1214 for hot-dip galvanised coatings on threaded fasteners.
A general introduction to standards in New Zealand is available here:
https://www.standards.govt.nz/
When sourcing AS/NZS 1252 assemblies, it is important that:
- Bolts, nuts, and washers are supplied as matched sets
- All components are compatible in strength and coating
- Documentation shows compliance with the edition of the standard required by your project specification
2.3 ASTM F3125 Grade A325 and similar standards
In North America and many international projects, you often see ASTM F3125 Grade A325 specified for heavy hex structural bolts. These quenched and tempered high-strength bolts are widely used in building and bridge construction. Many drawings still use the older designation ASTM A325, but in practice this has been combined into F3125.
When purchasing these bolts, clarify:
- Whether the project accepts F3125 Grade A325
- Which coatings are required (plain, mechanically galvanised, hot-dip galvanised)
- Which nuts and washers must be paired with the bolts
You can find a detailed description of the standard here:
https://www.astm.org/f3125-19.html
3. Understanding Bolt Strength and Property Classes
3.1 What “8.8” or “10.9” means
A property class such as 8.8 describes two key values:
- The first number (8) × 100 gives the approximate minimum ultimate tensile strength in MPa (800 MPa).
- The product of the two numbers (8 × 0.8 = 6.4) × 100 gives the minimum yield strength in MPa (640 MPa).
Higher property classes allow smaller diameters or fewer bolts, but they also require stricter control over installation and compatibility with connected materials. Very high property classes such as 12.9 are usually not used in structural steel connections because they can be more brittle and more sensitive to hydrogen embrittlement.
3.2 Choosing an appropriate property class
When selecting steel structure bolts, consider:
- Design codes and engineer requirements – Structural standards and the project engineer will specify acceptable bolt strength ranges.
- Connection type – Friction-type joints often use high-strength preloaded bolts such as AS/NZS 1252 assemblies or ASTM F3125 bolts.
- Plate thickness and deformation limits – Thin plates may suffer bearing damage before a very high-strength bolt yields.
- Availability – Common property classes like 8.8 are easier to source globally and replace during maintenance.
For many industrial buildings and general steel structures, property class 8.8 is a practical standard choice, while special situations may call for 10.9 or corrosion-resistant stainless steel grades.
4. Connection Types and Their Impact on Bolt Selection
4.1 Bearing-type vs slip-critical (friction) connections
Structural bolts in steel structures are often classified according to how the loads are transferred:
- Bearing-type connections – The bolt shank bears against the side of the hole. Slip is allowed within a certain limit. Bolt selection focuses on shear capacity and bearing strength.
- Slip-critical (friction-type) connections – The clamping force between plates prevents slip. Loads are transferred through friction at the faying surfaces. This requires high preload and specially prepared surfaces.
For slip-critical connections, you normally choose high-strength bolts (AS/NZS 1252, ASTM F3125 Grade A325, or equivalent) and a tightening method that achieves the specified preload. Faying surfaces may need to be blast-cleaned or treated to achieve the required slip factor; this should be coordinated with the coating system.
4.2 Shear, tension, and combined loading
Bolts can be loaded in:
- Shear – transverse to the bolt axis, typical for splice plates and many brace connections
- Tension – along the bolt axis, common in flange connections, tension bracing, and base plates
- Combined shear and tension – for example, moment connections where bolts resist both flange forces and shears
When the connection is dominated by tension, pay attention to:
- Thread position relative to the shear plane
- Required clamping force and tightening method
- Risk of relaxation due to gasket or coating compression
For high-tension applications, structural bolt assemblies with verified preload behaviour are usually specified.
4.3 Hole types and tolerances
Connection design may specify:
- Standard clearance holes
- Short-slot or long-slot holes
- Oversized holes with plate washers
Larger or slotted holes require special washers and sometimes different design resistance. When ordering bolts, confirm whether any special washers or plate washers are required, for example AS 1252 structural washers. A typical product is the AS1252 Structural Washer:
https://linkworldfast.com/product/as1252-structural-washer/
5. Sizing Steel Structure Bolts
5.1 Selecting diameter
Bolt diameter is determined mainly by:
- Design loads in shear and tension
- Plate thickness and edge distances
- Hole pattern and available space
- Practical issues such as wrench access and installation speed
Common diameters in steel building frames include M16, M20, M22, and M24. Heavier structures may use M30 or larger. The design engineer typically specifies the diameter based on code calculations, but purchasers should confirm that the diameter is commonly available in the required grade and coating.
5.2 Choosing bolt length
Bolt length must allow enough projection for:
- Plate stack thickness
- Washer and nut thickness
- Required thread engagement beyond the nut
A simple rule is that at least one full thread should be visible beyond the nut after tightening, but some standards specify more precise requirements. For preloaded structural bolts, manufacturers provide recommended grip ranges and thread lengths; your purchase order should specify the “grip” or “clamping thickness” when needed.
5.3 Thread type and pitch
For structural steel bolts, metric coarse threads according to ISO 261/262 are standard in many markets. Occasionally, fine pitch threads are used where higher tensile performance is needed or for special designs, but they are less common.
When working with international suppliers, clearly state:
- Thread type (metric coarse, UNC, UNF, etc.)
- Thread pitch if non-standard
- Tolerance class if the project requires it
6. Materials, Coatings, and Corrosion Protection
6.1 Base materials
Most carbon steel structural bolts are made from medium carbon or alloy steels suitable for heat treatment, following standards such as ISO 898-1, AS/NZS 1252, or ASTM F3125. For severe environments, stainless steel bolts (for example A2-70, A4-80) may be used, but their strength and behaviour differ from carbon steel high-strength bolts, so design codes must be followed carefully.
6.2 Coating options
Corrosion protection is critical in outdoor and coastal projects. Common systems include:
- Plain (black) steel – used indoors or where the structure is painted and protected in a controlled environment.
- Zinc electroplating – thin coating, suitable for indoor or mild outdoor conditions; not usually recommended for long-term exposure in aggressive atmospheres.
- Mechanical or zinc flake coatings – provide moderate to high corrosion resistance with controlled thickness, reducing the risk of thread fit problems.
- Hot-dip galvanizing (HDG) – thick, robust zinc coating for outdoor and marine environments; widely referenced by standards such as AS/NZS 1214 or ISO 10684.
When specifying hot-dip galvanised steel structure bolts, keep in mind:
- Coating thickness must be compatible with nut threads and tolerances.
- Nuts are often tapped oversize and lubricated to allow proper tightening.
- Matching galvanised washers are needed to protect the faying surfaces.
6.3 Compatibility with structural steel and other components
Different materials can create galvanic corrosion if they are not compatible. For example, stainless steel bolts in contact with carbon steel in a wet environment may accelerate corrosion of the carbon steel. In many structural applications, it is safer to keep similar materials and coating systems across the bolt assembly and connected plates.
When ordering from overseas, clarify:
- Base material of bolts, nuts, and washers
- Coating system and relevant standards
- Whether bolt assemblies are supplied fully finished (bolt + nut + washers) or as separate components
7. Installation Requirements and Quality Control
7.1 Pre-installation checks
Before installation, site teams should verify:
- Correct bolt type, grade, and coating for each connection zone
- Matching nuts and washers from the same assembly batch where required
- No visible damage, thread defects, or serious corrosion
- Correct bolt length for the plate stack
For high-strength preloaded assemblies, pre-installation verification testing is often specified, where sample bolts are tightened to a specified tension in a test rig.
7.2 Tightening methods
Common tightening methods for structural bolts include:
- Snug-tight plus turn-of-nut – bolts are first brought to snug-tight condition, then turned further by a specified angle.
- Calibrated torque wrench – torque values are established by testing and then applied in the field.
- Tension-control (TC) bolts – special bolts where a spline breaks off at a set tension; more common in some markets than others.
The chosen method influences lubrication requirements, tolerance of surface coatings, and training needs for workers.
7.3 Inspection and documentation
Quality control for steel structure bolts should include:
- Visual inspection of bolt head markings and lot identification
- Check of nut position and thread projection
- Confirmation of correct washer orientation (especially structural washers)
- Random verification of torque or tension, depending on the tightening method
Project documentation often requires test reports from the bolt manufacturer. When working with international suppliers, it is a good idea to review these documents before shipping and to clarify any special test requirements in advance.
8. Procurement Checklist for Steel Structure Bolts
When you place an order for steel structure bolts with an overseas supplier, clear communication helps avoid mistakes and extra costs. The following checklist can be used when sending your RFQ, drawings, or bill of materials.
8.1 Basic technical specification
For each bolt item, specify:
- Standard: for example AS/NZS 1252 assembly, ASTM F3125 Grade A325, or ISO 898-1 property class 8.8
- Bolt type: heavy hex, hex, countersunk, etc.
- Diameter and length: for example M20 × 80 mm
- Thread details: metric coarse, UNC, or others; full or partial thread
- Property class / grade: 8.8, 10.9, A325, etc.
- Coating: plain, zinc plated, mechanically galvanised, hot-dip galvanised (and the target standard such as AS/NZS 1214 or ISO 10684)
- Required nut and washer types, including structural washers if needed
8.2 Assembly and packaging
Clarify:
- Whether bolts, nuts, and washers should be packed as matched assemblies or separately
- Required marking on cartons or small boxes (size, grade, project code)
- Any special small packing, such as branded cardboard boxes or plastic boxes
- Palletisation or container loading preferences
Linkworld can combine cold-formed bolts, washers, and other metal parts into one shipment and can discuss flexible small packing based on your warehouse and job-site needs. You can see the overall product range here:
https://linkworldfast.com/products/
8.3 Testing and quality documents
Discuss in advance which quality documents you require, for example:
- Mechanical test reports according to ISO 898-1, AS/NZS 1252, or ASTM F3125
- Coating test reports (galvanizing thickness, adhesion tests)
- Dimensional inspection records for critical sizes
Agreeing on the scope of testing and reporting before production helps both sides plan the schedule and avoid delays.
8.4 Logistics and stock planning
For projects with phased construction, you may want to:
- Split deliveries into several batches by area or stage
- Keep a buffer stock of common sizes in your warehouse
- Combine structural bolts with related product categories such as concrete fasteners or rigging components in the same container
A consolidation service is useful if you source multiple fastener types from one supplier. For example, structural bolts, AS1252 washers, concrete screws, and safety chains can all be shipped together to reduce handling costs. One example is the Safety Chain product:
https://linkworldfast.com/product/safety-chain/
9. Example: Bolt Selection for a Steel Warehouse Project
Imagine you are procuring fasteners for a steel warehouse near the coast in Australia. The structure includes primary frames, bracing, secondary purlins, and accessory steel.
A possible bolt selection strategy could be:
- Primary frame connections (moment and bracing joints)
- M20 and M24 high-strength structural bolt assemblies to AS/NZS 1252.1
- Property class 8.8, hot-dip galvanised according to AS/NZS 1214
- Slip-critical connections at key bracing joints, bearing-type elsewhere
- Secondary steel (purlins and girts)
- Self-drilling or self-tapping screws complying with AS 3566, with a corrosion category suitable for the location
- For example, batten screws or roofing screws from the screws category:
https://linkworldfast.com/product-category/screws/
- Connection of accessories and safety components
- Galvanised hex bolts in property class 8.8
- Safety chains with compatible coating, such as the Safety Chain mentioned above
In this scenario, the purchase order would clearly separate:
- AS/NZS 1252 structural assemblies (bolts + nuts + structural washers)
- General hex bolts and nuts according to ISO 898-1 property class 8.8
- Self-drilling screws and other special fasteners
The supplier can then plan production and sourcing to match the project phases, and the site team can easily identify which fasteners belong to each connection type.
10. Working With Linkworld for Steel Structure Bolts
Jiaxing Linkworld Fastener is based in one of China’s major fastener hubs and combines its own cold forming and machining capability with long-term partner workshops. This setup supports both standard fasteners and drawing-based parts, as well as small-batch and consolidated orders.
For steel structure projects, Linkworld’s range includes:
- Structural assemblies such as AS1252 Structural Washers and matching bolts and nuts
- Hex bolts and other structural fasteners in property classes like 8.8 and 10.9 – see examples here:
https://linkworldfast.com/product/hex-bolts/ - Concrete fasteners, screws, rigging products, and various customised metal components that can be packed and shipped together with your bolt orders – overview here:
https://linkworldfast.com/products/
If your project requires special bolts based on drawings or non-standard dimensions, you are welcome to send detailed specifications, including connection details and coating requirements. The engineering and sales team can discuss options based on your drawings, expected environment, and installation method, aiming to provide a practical solution that matches your steel structure design.
You can learn more about the company background and manufacturing capabilities here:
https://linkworldfast.com/about-us/
11. FAQ: Steel Structure Bolts
Q1: Can I mix bolts, nuts, and washers from different suppliers in one connection?
It is not recommended for critical structural connections. High-strength bolt assemblies are designed and tested as a set, so mixing components from different sources may change the friction behaviour, nut stripping strength, or torque–tension relationship. For important joints such as slip-critical or preloaded connections, it is safer to use matched assemblies from one source and keep the lot identification for inspection.
Q2: How many spare bolts should I order for a project?
The design quantity usually does not include waste, damage, or future modifications. A common practice is to add 3–5% spare bolts, nuts, and washers for each size, depending on project complexity and accessibility. For remote sites or long-term projects, you may choose a higher percentage to avoid downtime if some items are lost or rejected during inspection.
Q3: When should I choose stainless steel bolts instead of carbon steel?
Stainless steel bolts are often used in highly corrosive environments such as marine structures, chemical plants, or food factories where frequent washing occurs. However, stainless steel grades such as A2-70 or A4-80 have different mechanical properties compared with high-strength carbon steel bolts, and they are usually not used as direct replacements for AS/NZS 1252 or ASTM F3125 structural assemblies. Before switching to stainless steel, check the design code and confirm with the project engineer that the connection capacity and detailing are still adequate.
12. Summary and Next Steps
Selecting the right steel structure bolts is not only about choosing a diameter and length. It involves understanding standards such as ISO 898-1, AS/NZS 1252, ASTM F3125/A325, and AS/NZS 1214; matching property class and coating to the environment; and coordinating installation and inspection procedures with your site teams.
When you plan a new project or review your current specifications, consider:
- Which standards and grades are required for each connection type
- How corrosion exposure affects the coating choice
- Whether bolts, nuts, and washers will be supplied as complete assemblies
- What testing and documentation your project needs
- How to combine different fastener types into a clear, efficient procurement plan
If you would like to discuss steel structure bolts, send your drawings, or build a mixed fastener list for your next project, you are very welcome to contact the Linkworld team. You can visit the homepage at
https://linkworldfast.com/
browse the product range at
https://linkworldfast.com/products/
or send an inquiry via
https://linkworldfast.com/contact/
or by email at info@linkworldfast.com.