Choosing the Right Nuts for High Tensile Bolts

High tensile bolts get a lot of attention in engineering and construction, but the nuts holding those bolts in place are just as critical. If the nut grade is too low, the nut can strip before the bolt reaches its design tension. If the nut grade and standard do not match the bolt, you may have hidden weaknesses in your connection, especially in high-strength or slip-critical joints.

For overseas buyers, engineers and distributors supplying projects in Australia, New Zealand and other markets, understanding nut grades is an important part of sourcing high tensile fasteners. This guide explains what nut grades mean, how they relate to bolt grades, which standards apply, and how to choose nut grades that match your applications. We will also look at coatings, locknuts and practical purchasing tips when you work with a fastener manufacturer.

1. What does “nut grade” actually mean?

When people talk about nut grade or nut class, they are usually referring to the mechanical property class of the nut. For metric steel nuts, these property classes are defined in ISO 898-2 and related standards. 国际标准化组织+1

ISO 898-2 specifies:

  • The property classes for carbon and alloy steel nuts (for example 5, 8, 10, 12).
  • The styles (thin, regular, high) and minimum nut height for each style.
  • The proof load values for each property class and size.
  • Test methods, marking and designation rules.

The proof load is a key concept. Nut loadability is primarily checked by proof load: the nut is tightened against a hardened mandrel to a specified load, and it must not strip. 国际标准化组织

In the inch system, the most common nut grading standard is ASTM A563. It defines multiple grades such as A, B, C, D, DH and others, each with different strength levels and typical applications. Portland Bolt+2Baden Steelbar & Bolt Corp.+2

In everyday language, buyers often say “Grade 8 nut” or “Grade 10 nut”, but it is better to use the full standard designation (for example, “ISO 898-2 property class 10 nut” or “ASTM A563 Grade DH heavy hex nut”) so there is no confusion.

2. How nut grade relates to bolt grade

Nut grade must always be compatible with the bolt grade and material. Nuts are designed so that, when correctly paired with bolts, the bolt will reach its design tension without the nut failing.

Metric bolt and nut combinations

For ISO metric fasteners, ISO 898-2 includes a table linking nut property classes to compatible bolt property classes according to ISO 898-1. 国际标准化组织+1

In simplified form:

  • Property class 8 nuts are used with bolts of property class 8.8 or lower, within the permitted size range.
  • Property class 10 nuts are used with bolts of property class 10.9 or lower.
  • Property class 12 nuts are used with the highest strength bolts such as 12.9 where allowed by the standard and nut style.

The property class numbers for bolts, such as 8.8 and 10.9, follow a simple rule: the first number multiplied by 100 gives the nominal tensile strength in MPa, and the second number (multiplied by ten) gives the ratio of yield strength to tensile strength. Hague Fasteners Limited+1

Nuts are not marked with a decimal, but their property class must provide sufficient proof load so that the bolt can be fully tensioned without stripping the nut. For example, if you use a property class 10.9 bolt, you normally need at least a property class 10 nut, and the nut height must meet the requirements for that class.

Inch bolt and nut combinations

In imperial systems used in some global projects, ASTM A563 provides guidance on matching nut grades to bolt grades such as ASTM A325, A490, or SAE grades. Technical references list recommended combinations, for example using ASTM A563 Grade DH heavy hex nuts with high-strength structural bolts. Portland Bolt+2TorqBolt+2

For AU/NZ buyers, you will often see both metric and inch specifications in different parts of a project. It is very important to keep them separate and avoid mixing nuts and bolts of different systems.

3. Standards most relevant to nut grade in AU/NZ projects

Australia and New Zealand follow metric standards for most construction fasteners, but some projects also use inch-based structural fasteners or imported equipment. Several standards are especially important when choosing nut grades.

ISO 898-2 – Mechanical properties of nuts

ISO 898-2 is the core international standard for mechanical properties of carbon and alloy steel nuts, covering property classes 04, 05, 5, 6, 8, 10 and 12, and three nut styles (thin, regular and high). 国际标准化组织+1

This standard applies to a wide range of general engineering and structural nuts used with ISO 898-1 bolts. Many national standards and product specifications are aligned with ISO 898-2, including AS/NZS standards for nut proof loads.

AS/NZS 1252 and AS/NZS 4291.2 – Structural assemblies and nut proof loads

High-strength structural bolt assemblies for steelwork in AU/NZ are covered by AS/NZS 1252 (Parts 1 and 2), which specify bolt, nut and washer assemblies rather than individual components. 交通运输和主要道路部+3Scribd+3Steel Construction New Zealand+3

Mechanical properties for many metric nuts, including proof loads for coarse-thread nuts, are aligned with ISO 898-2 and related standards such as AS/NZS 4291.2. Guidance from steel construction organisations stresses that nuts must be supplied as part of complete bolt assemblies to AS/NZS 1252, not mixed from unrelated stocks. steel.org.au+1

ASTM A563 – Carbon and alloy steel nuts

ASTM A563 covers carbon and alloy steel nuts for general structural and mechanical uses, defining multiple grades and strength levels. It is highly relevant to inch-size fasteners and to projects that import US-standard hardware. Portland Bolt+1

If an AU or NZ project specifies ASTM bolts such as A325 or A490, you should match them with appropriate ASTM A563 nut grades, not with ISO 898-2 metric nuts.

4. Matching nut grade to high tensile bolt applications

Now we can look at how nut grade choices play out in real applications.

4.1 Structural steel bolting

For structural steelwork in AU/NZ, high-strength bolts, nuts and washers are usually supplied as assemblies to AS/NZS 1252, with defined property classes and coatings. Scribd+2Steel Construction New Zealand+2

In these assemblies:

  • Nut grade is chosen so that the nut will not strip when the bolt is fully tensioned.
  • The whole assembly (bolt + nut + washer) is tested as a set.
  • Coating systems such as hot dip galvanizing are considered in the design and testing.

As a buyer, the safest approach is to specify the required AS/NZS 1252 assembly and construction category rather than trying to choose nut grade separately. For example, you might choose M20 high-strength structural bolt assemblies that include appropriately graded nuts and structural washers.

Example structural washer product:
https://linkworldfast.com/product/as1252-structural-washer/

These assemblies are typically used with structural hex bolts such as:
https://linkworldfast.com/product/hex-bolts/

Both items sit within the broader category for bolts, nuts and washers:
https://linkworldfast.com/product-category/bolts-nuts-washers/

4.2 General high tensile bolts (8.8 and 10.9)

In many machines, vehicles, mining equipment and heavy-duty fixings, high tensile bolts of property class 8.8 or 10.9 are used outside of formal structural steelwork.

Some common rules of thumb:

  • Class 8.8 bolts are normally paired with class 8 nuts (or higher) that comply with ISO 898-2.
  • Class 10.9 bolts require class 10 nuts of adequate height and proof load.
  • If there is any doubt about dynamic loads or tensioning method, using a higher nut class (for example a 10 nut with an 8.8 bolt) can provide extra safety margin, provided the nut meets the relevant standard and style.

When you are ordering high tensile bolts from a supplier like Linkworld, you can group the bolts, nuts and washers into kits or assemblies, or include them together on your BOM so that the supplier can select compatible nut grades.

4.3 Stainless and special material nuts

For stainless steel applications, nut grade is handled through different standards (for example ISO 3506 property classes such as A2-70, A4-80). These have their own compatibility rules between bolts and nuts. The same principles apply:

  • Nut proof load must be sufficient for the bolt’s tensile strength.
  • Height and style must meet the relevant standard.
  • Coating and lock features (if any) must be considered.

If your project involves special materials, it is usually best to share the design standard and desired mechanical class with your supplier, who can recommend an appropriate nut grade and standard.

5. Nut geometry: style, height and thread

Nut grade is not only about material strength. Geometry also matters.

5.1 Nut style and height

ISO 898-2 defines three main nut styles: thin (style 0), regular (style 1) and high (style 2), each with a minimum height as a proportion of nominal diameter. Itech Standards

High-strength applications typically require regular or high nuts to ensure that the thread engagement is sufficient. Thin nuts may be suitable as jam nuts or locknuts but are not usually used as the main load-bearing nut for high tensile bolts.

When you choose a nut grade, make sure you also consider:

  • Hex size (width across flats)
  • Nut height relative to bolt diameter
  • Any special shape (flange nuts, cap nuts, coupling nuts)

5.2 Thread fit and tolerance

Nuts and bolts must share the same thread standard and tolerance class, for example ISO metric coarse thread with defined tolerance. Mismatched thread standards (for example UNC vs metric) or poor thread tolerances can lead to reduced thread engagement, higher stress and early failure.

High-strength nuts are manufactured with tighter controls on threads and are tested with proof load methods to ensure loadability. Testing requirements for nuts under ISO 898-2 include proof load tests and hardness checks. ZwickRoell Materials Testing+1

For buyers, it is important to specify thread standard, tolerance class and any special requirements (such as interference fit or oversize threads for galvanized nuts) in your RFQ.

6. Coatings, galvanizing and nut grade

Coating choice strongly affects nut performance, especially for hot dip galvanized fasteners.

6.1 Hot dip galvanized nuts

When nuts are hot dip galvanized, the coating adds thickness on the threads. To allow proper assembly, nut threads are usually tapped oversize before galvanizing. ASTM A563 and related standards include tables of over-tapping allowances for galvanized nuts and specify which nut grades can be galvanized. Portland Bolt+1

Key points for galvanized nuts:

  • Use nut grades that are approved for galvanizing and over-tapping under the relevant standard.
  • Make sure bolt and nut threads are compatible after coating (for example bolt thread tolerance with oversize nut thread).
  • Remember that friction is affected by coating and lubrication; this will influence torque-tension relationships in high-tensile bolts.

6.2 Zinc flake and other coatings

For some high-performance applications, zinc flake or mechanical zinc coatings are used instead of hot dip galvanizing. These thin, uniform coatings reduce the risk of thread interference and can give more consistent friction factors.

If you are using friction-type joints or precise torque-tension control, discuss coating and lubrication with your supplier. Nuts, bolts and washers should share a coordinated coating system and be tested as assemblies where necessary.

6.3 Plain and plated finishes

In internal dry environments, plain (black) or zinc plated nuts may be sufficient. The nut grade (property class) is still important, but corrosion risk is lower. For outdoor or marine conditions, higher-level coatings or stainless materials are typically required.

7. Locknuts, prevailing torque and nut grade

In many high tensile bolt applications, preventing loosening from vibration is just as important as static strength. Several nut types support this:

  • Nylon insert locknuts (nyloc nuts) – Provide prevailing torque via a polymer insert.
  • All-metal prevailing torque nuts – Use distorted threads or slotted designs to create friction.
  • Flange nuts – Distribute load over a larger bearing area and can include serrations.

For these products, grades and standards still apply. For example, ISO 7042 covers prevailing torque all-metal hexagon high nuts in property classes 5, 8, 10 and 12. 永久和平发展协会

When choosing locknuts for high tensile bolts:

  • Check that the nut grade (property class) matches or exceeds the bolt grade requirements.
  • Confirm the temperature range of nylon inserts; high temperatures can reduce their effectiveness.
  • Ensure that prevailing torque values are compatible with the tightening method and available tools.

If you are working with multiple nut types in one project (for example standard heavy hex nuts and nylon insert locknuts), clear labelling and packing will help installers select the correct nut for each location.

8. Practical RFQ checklist: what to specify for nut grade

To get the right nuts for your high tensile bolts, your enquiry should include more detail than just “high tensile nut” or “grade 8 nut”. Here is a checklist you can adapt for your own RFQs:

  1. Standard and grade
    • ISO 898-2 property class (for example 8, 10 or 12)
    • Or ASTM A563 grade (A, C, DH, etc) for inch series
    • Any national standard references (AS/NZS, EN, etc)
  2. Nut style and geometry
    • Hex regular or high, flange nut, cap nut, coupling nut, etc
    • Nominal size (M16, M20, 3/4″, etc)
    • Nut height or style (thin, regular, high)
  3. Thread type
    • Metric coarse, metric fine, UNC, UNF, etc
    • Tolerance class and over-tapping requirements for galvanizing
  4. Coating and lubrication
    • Plain, zinc plated, mechanical zinc, zinc flake, hot dip galvanized
    • Any requirement for lubricated nuts or waxed washers
  5. Bolt combination
    • Bolt grade and standard to be used with the nuts
    • Application (snug-tight, fully tensioned, slip-critical, dynamic loading)
  6. Testing and documentation
    • Required test reports (proof load, hardness, coating thickness, torque-tension)
    • Third-party or in-house testing acceptance
    • Traceability level (batch number, heat number)
  7. Packing and labelling
    • Inner pack and carton quantities
    • Maximum carton weight
    • Required label fields (size, grade, coating, standard, batch, customer part number)

Including this information makes it much easier for your supplier to select the correct nut grade and avoid substitutions that may not be suitable.

9. How a supplier can help with nut grade selection

Selecting nut grades is not something buyers have to do alone. A fastener partner that combines manufacturing and sourcing experience can support you at several levels.

A supplier like Linkworld, for example, focuses on cold formed parts such as bolts, nuts and washers, while also integrating machining, stamping, rigging and other components from partner factories. The in-house QC team and inspection facilities allow them to check dimensions, mechanical properties and coatings against the specified standards.

When you share your project information, the supplier can:

  • Suggest compatible nut grades for the bolt grades and standards you specify.
  • Propose complete assemblies (bolt + nut + washer) that match AS/NZS or ISO requirements.
  • Run trial assemblies and torque-tension tests where needed. linkworldfast.com+2ZwickRoell Materials Testing+2

You can browse typical related products here:

Having nuts, bolts and washers from the same source can simplify quality control and make it easier to manage mixed pallets, labels and packing formats.

10. Example scenarios: choosing nut grade in real projects

To make this more concrete, here are a few practical scenarios.

Scenario 1: Structural steel frame in coastal Australia

  • Bolts: High-strength structural assemblies M20 to AS/NZS 1252, hot dip galvanized.
  • Requirement: Slip-critical joints in a C4 corrosion environment.

In this case, nut grade is determined by the structural assembly standard. You would order assemblies that include suitably graded heavy hex nuts and structural washers, tested as a set. Coating, lubrication and friction factors would follow design assumptions for slip-critical joints. External design and technical guides from steel industry bodies emphasise that such assemblies should be supplied and tested as complete sets to maintain performance. steel.org.au+2新南威尔士交通局+2

Scenario 2: Mining equipment with 10.9 bolts

  • Bolts: M24 × 10.9 hex bolts, zinc flake coated.
  • Application: High vibration, cyclic loads.

Here, you might specify ISO 898-2 property class 10 high nuts of suitable height, possibly all-metal prevailing torque nuts if loosening is a concern. If galling or wear is likely, you could consider through-hardened washers and locknut arrangements.

Scenario 3: Imperial structural bolts imported from the US

  • Bolts: 3/4″ A490 structural bolts.
  • Application: Industrial structure with preloaded connections.

You would select heavy hex nuts that comply with ASTM A563 Grade DH, hot dip galvanized if required. Manufacturer technical pages on ASTM A563 explain the mechanical requirements and typical grade combinations for these high-strength applications. Portland Bolt+2Baden Steelbar & Bolt Corp.+2

In all scenarios, the key point is that nut grade is chosen in combination with bolt grade, standard, coating and joint type, not in isolation.

11. Working with your supplier: communication tips

To get the most from your nut and bolt supplier, consider these communication steps:

  • Share drawings and connection details – Even simple sketches help clarify bolt size, number of nuts (for example double-nut arrangements), washer type and available space.
  • Explain the codes and standards – Tell the supplier whether the project follows AS/NZS, ISO, EN, ASTM or a combination.
  • Discuss installation methods – Impact wrench only, calibrated torque, turn-of-nut, or direct tension indicators; this can influence nut grade and coating choices.
  • Talk about packing and storage – Nuts can be supplied bulk, in small boxes, or in kits together with bolts and washers, depending on how they will be used on site.

Linkworld can also support small packing and mixed-item cartons for distributors and retailers, which is useful when you want to provide complete bolt-nut-washer sets to your customers. You can explore the overall product and service range here:
https://linkworldfast.com/products/

For company background:
https://linkworldfast.com/about-us/

For enquiries, BOMs and drawings:
https://linkworldfast.com/contact/

12. Conclusion: treat nut grade as part of the whole bolted system

Choosing the right nuts for high tensile bolts is not just an academic exercise. Nut grade affects whether you can reach the required bolt tension without stripping threads, maintain preload over time, and keep joints safe under dynamic and environmental loads.

By understanding nut property classes, the standards behind them, and how they match to bolt grades, you can make better purchasing decisions and avoid many common fastener problems. When you work closely with a manufacturer or supplier who understands both international standards and local AU/NZ project requirements, you can select nut grades, coatings, locknut styles and packing options that support your projects from design through to installation.

If you are reviewing your current fastener list or planning a new project that uses high tensile bolts, you are welcome to send your requirements, drawings and packing ideas to the Linkworld team via https://linkworldfast.com/contact/ or email info@linkworldfast.com. They can work with you to choose nut grades and complete fastener assemblies that match your standards, tools and working conditions.

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