Stainless Metric Flat Head Socket Cap Screws

Metric Stainless Steel Flat Head Socket Cap Screws — A2-70 and A4-70, DIN 7991

Shop Metric Stainless Flat Head Socket Cap Screws

Metric stainless flat head socket cap screws conform to DIN 7991 with a 90° included countersink angle, available in A2 (equivalent to 304/18-8 stainless) and A4 (equivalent to 316 stainless) property classes. They provide corrosion resistance in applications where metric thread standards are required and the environment precludes use of alloy steel. The 70 designation in A2-70 and A4-70 indicates a minimum tensile strength of 700 MPa (~101,500 PSI) — lower than Class 12.9 alloy, so verify load requirements before substituting.

Understanding A2 and A4 Property Classes

A2-70 uses 304/18-8 stainless steel alloy (18% chromium, 8% nickel) with a minimum tensile strength of 700 MPa. This is the standard choice for general corrosion resistance in non-marine environments — food service, laboratory equipment, outdoor hardware not exposed to salt water or chlorides.

A4-70 uses 316 stainless steel, adding approximately 2–3% molybdenum to the A2 base alloy. The molybdenum significantly improves resistance to chlorides and pitting corrosion. A4 is the correct choice for marine applications, coastal outdoor structures, chemical processing equipment, and any environment with significant chloride exposure. A4-80 (800 MPa tensile) is available for higher-strength requirements in corrosive environments.

Frequently Asked Questions

What does A2-70 mean for metric stainless flat head socket cap screws?
A2 designates the stainless steel alloy — approximately equivalent to 304/18-8 stainless (18% chromium, 8% nickel). The 70 indicates a minimum tensile strength of 700 MPa (~101,500 PSI). A2-70 is the standard property class for stainless metric fasteners in general corrosion-resistant applications.

What is the difference between A2 and A4 stainless metric fasteners?
A4 stainless (equivalent to 316 SS) adds approximately 2–3% molybdenum to the A2 alloy. This provides significantly better resistance to chlorides, salt water, and acidic solutions. Use A4 for marine, coastal, or chemical environments. Use A2 for general corrosion resistance where chloride exposure is not a primary concern.

What countersink angle do metric stainless flat head socket cap screws use?
90° included angle per DIN 7991, the same as metric alloy flat head socket cap screws. This is different from inch-series (82° per ASME B18.3). Metric and inch flat head socket cap screws are not interchangeable — confirm your countersunk hole angle before ordering.

Are A2-70 stainless metric flat head socket cap screws as strong as Class 12.9 alloy?
No. A2-70 has a minimum tensile strength of 700 MPa (~101,500 PSI), compared to 1,220 MPa (~177,000 PSI) for Class 12.9 alloy. If maximum clamping force is required in a metric countersunk application and the environment permits, Class 12.9 alloy is significantly stronger.

Metric stainless flat head socket cap screws are typically used alongside other A2 or A4 stainless metric fasteners to maintain consistent material throughout the assembly — mixing stainless and carbon steel in wet or marine environments can accelerate galvanic corrosion. For metric countersunk applications where maximum strength is required and corrosion is not a concern, see metric alloy flat head socket cap screws (Class 12.9, DIN 7991). The full flat head socket cap screw selection is available through the Flat Head Socket Cap Screw category.