A2-70 vs A4-80 Stainless Steel Bolts: Differences and Substitution Checks

A2-70 and A4-80 differ in two aspects: stainless steel grade and mechanical performance grade. A2 and A4 indicate the grade of austenitic stainless steel; 70 and 80 indicate attribute categories. A4-80 has higher minimum tensile and verification stress values for applicable products than A2-70, but it is not automatically replaceable.

For buyers, the decision is not just about whether to order stronger bolts. The required materials, exposure conditions, mating components, and installation procedures must comply with approved specifications.

What do A2-70 and A4-80 mean?

The name has two separate parts:

• A2 or A4: Stainless steel grade. A2 is usually associated with 304 stainless steel, while A4 is usually associated with 316 stainless steel containing molybdenum. These are useful series comparisons, not precise material specifications.
• 70 or 80: Mechanical performance level. This number is related to the specified mechanical properties and is not related to the chemical or corrosion resistance level of stainless steel.

Both of these parts are important. Querying '316 bolt' may result in undefined attribute categories. It has not been determined whether A2, A4, or other stainless steel grades are required for the inquiry of "80 grade bolts".

A2-80 and A4-70 also appear in the ISO 3506 system. This helps explain why levels and attribute categories should not be considered as one level: changing A2 to A4 and changing 70 to 80 are different decisions. The availability of the required products and sizes still needs to be confirmed.

2. A2-70 vs A4-80: Comparison Table

The mechanical values are for applicable full-loadability bolts, screws and studs under ISO 3506-1. Check the specified edition, diameter, thread and product geometry before applying them. Reduced-loadability products require separate assessment. The figures are not elevated-temperature design values.

These minimum properties do not give the allowable load of a joint, a tightening torque, or a service-life prediction. Connection capacity also depends on geometry, engagement, loading and the connected components. The British Stainless Steel Association's fastener guide provides the grade and property-class background for this comparison.

3.Can A4-80 replace A2-70?

Not only because its minimum mechanical value is higher. If the approved drawings specify A2-70, the recommendation to supply A4-80 will change the stainless steel grade and performance grade.

Before accepting the replacement, please confirm:

1. Specify the product. Check drawing revisions, dimensional standards, diameter, pitch, length, and thread length.
2. Joint requirements. Have the responsible technical reviewer evaluate material and mechanical performance changes based on the connection, not just the bolt catalog description.
3. Complete assembly. Check nuts, washers, thread engagement, surface condition, and any specified lubricants or tightening procedures.
4. Approval records. Before placing an order, identify the proposed deviations in the quotation and obtain approval through the project approval process.

For example, the quotation A4-80 and A2-70 drawings should clearly indicate the differences. Listing only the project as 'stainless steel bolts' will conceal the changes, rather than resolving them.

In areas where specifications are still being developed, separate the questions: which grade of stainless steel is suitable for exposure, and which performance grade is required for joints? Higher numbers do not answer the material selection question.

4.Does A4-80 always provide better corrosion performance?

The A4 grade, rather than the "80" performance grade number, is related to the corrosion characteristics of its material family. Molybdenum can enhance resistance to pitting and crevice corrosion, but A4 is not immune to corrosion in all environments.

Describe actual usage conditions: exposure to salt or chemicals, temperature, wetting frequency, standing water, sediment, cracks, and cleaning conditions. The shaded coastal air, repeated saltwater splashes, and seawater immersion are different exposures; 'Marine' itself is not a complete material specification.

For the broader choice between stainless steel and zinc-coated carbon steel, see HDG fasteners vs stainless steel for marine and coastal steelwork. If the fasteners will contact galvanized steel, also review the galvanic-corrosion considerations for stainless steel bolts and galvanized steel.

5. Check nuts, washers, and installation conditions

Designate matching components separately

According to ISO 3506-2, stainless steel nuts have separate mechanical requirements. The tensile stress and verification stress values of bolts are not the acceptance values of nuts. Nut style, height, and thread engagement can also affect assembly; Do not assume that any nut with the same nominal diameter is suitable.

Specify the nut standard, grade, property class and style, plus the washer material and dimensions required by the drawing. For stud a

ssemblies, our 316 stainless steel double-ended stud bolt guide covers the product configuration and enquiry details.

Resolve wear issues without replicating universal torque

Austenitic stainless steel threaded components may experience wear: adhesive wear may damage the mating surface and cause jamming. Choosing A4-80 itself does not establish a method to prevent wear and tear.

Approved lubricants or surface treatments can reduce risks, but they can also affect the friction and torque preload relationship. Use installation requirements developed for actual assembly. Without technical review, torque values shall not be transmitted from dry, coated, or lubricated connections.

What content should be included in A2-70 or A4-80 queries?

Keep two parts of the name visible throughout the entire inquiry, quotation, and purchase order.

Ask the supplier to identify deviations and confirm the proposed supply scope in writing. Do not assume that every size, property class or document type is available or included. At delivery, use the order as the reference for matching fastener markings, packages and test reports.

Stainless Steel Product Options for Your Enquiry

Hotop Fasteners' stainless steel range includes hex head bolts, hex flange bolts and socket head cap screws. Start with the product form required by the drawing; these forms are not interchangeable simply because the grade designation is the same.

The exact size, grade and configuration should be defined as one order item, not selected independently from separate lists. Material names such as 304, 316 or 316L do not replace the required property class.

Packaging options across these product families include bags, cartons and, for selected products, pallets and customized labels or packaging. Drawing-based and sample-based customization can be discussed for suitable products. Minimum order quantities and delivery schedules depend on the selected product, configuration and packaging; there is no single term that should be applied to every stainless steel fastener.

Where EN 10204 3.1 documentation is required, state it in the enquiry and agree the document scope, product or lot identification, cost and delivery timing in the quotation.

Send your drawing and quantity schedule to Hotop Fasteners. Include the required grade and property class, mating components, packaging and document requirements, and identify any substitution still awaiting technical approval.