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

The stainless steel grades and mechanical performance grades of A2-70 and A4-80 are different. A4-80 has a higher specified minimum mechanical performance for applicable products, but it is not an automatic substitute for A2-70. The buyer should check the approved specifications, exposure conditions, and complete assembly before placing an order.

What do A2-70 and A4-80 mean?

The name consists of two separate parts: A2 or A4 represents the stainless steel grade. A2 is usually associated with 304 stainless steel, while A4 is usually associated with 316 stainless steel containing molybdenum. These are series comparisons, not exact material specifications.

70 or 80 represents the mechanical performance level. It does not describe the chemical properties of stainless steel, nor does it provide corrosion resistance levels.

A2-80 and A4-70 also exist in the ISO 3506 system. Therefore, changing the material grade and changing the attribute category are separate decisions.

A2-70 and A4-80: Comparison Table

These values apply to relevant full load bolts, screws, and studs under ISO 3506-1. Check the specified version, diameter, thread, and geometric shape. They are not joint load capacity, tightening torque, or high-temperature design values.

For technical background, please refer to the Stainless Steel Fasteners Guide by the British Stainless Steel Association.

Can A4-80 replace A2-70?

This is not only because its minimum intensity value is higher. If the drawing specifies A2-70, providing A4-80 will change the material grade and characteristic category.

Before accepting the replacement, please confirm:

• Product standards, drawing revisions, diameter, pitch, length, and thread length.
• Material and mechanical requirements for joints.
• Compatible nuts, washers, thread engagement, and installation conditions.
• Obtain written approval through the substitution or deviation process of the project.

The quotation for A4-80 and A2-70 drawings should clearly indicate the differences. Describing both as' stainless steel bolts' does not solve this change.

Check Corrosion Exposure and Assembly Conditions

The A4 grade, rather than the “80” number, relates to its material-family corrosion characteristics. Molybdenum can improve resistance to pitting and crevice corrosion, but A4 is not suitable for every chloride-containing environment.

Assess salt or chemical exposure, temperature, wetting, trapped water and crevices. Coastal air, saltwater splash and seawater immersion are different conditions. For wider material selection, read HDG fasteners vs stainless steel for marine and coastal steelwork. Mixed-metal connections also require a galvanic-corrosion review.

Specify nuts and washers separately. Stainless steel nuts have their own requirements under ISO 3506-2; bolt tensile values are not nut acceptance values. For stud configurations, see our 316 stainless steel double-ended stud bolt guide.

Stainless steel threads can also experience galling and seizure. Approved lubrication may reduce risk but changes friction and the torque-preload relationship. Use the installation procedure established for the actual assembly rather than copying a generic torque.

Choose a Product and Prepare Your Enquiry

Hotop Fasteners’ stainless steel product range includes:

• DIN 933 / DIN 931 stainless steel hex bolts: A2-70, A4-70 and A4-80 options.
• DIN 6921 stainless steel hex flange bolts: A2-70 and A4-80 options.
• DIN 912 stainless steel socket head cap screws: A2-70, A4-70 and A4-80 options.

Confirm the exact size, grade and configuration together. Include the drawing or standard, dimensions, mating components, exposure conditions, quantity, packaging and required documents. MOQ, customization and delivery arrangements depend on the selected product.

If EN 10204 3.1 documentation is required, specify its scope and identification requirements in the enquiry. At delivery, check the order against the fastener markings, packages and test reports.

Send your drawing and quantity schedule to Hotop Fasteners to discuss the required specification, supply conditions and any proposed substitution.