Alloy Metric Flat Head Socket Cap Screws

Metric alloy flat head socket cap screws conform to DIN 7991 and ISO 10642 — the metric equivalents of the inch-series ASME B18.3 standard. The key distinction from inch-series: metric flat head socket cap screws use a 90° included countersink angle, not the 82° angle used for inch fasteners. The mating countersunk hole must be drilled and countersunk to 90° — confirm your tooling before ordering if you are transitioning between inch and metric hardware. Eugene Fastener stocks metric alloy flat head socket cap screws in a full range of metric sizes from stock in Eugene, Oregon.

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Metric Alloy Flat Head Socket Cap Screws — DIN 7991, 90° Countersink

Shop Metric Alloy Flat Head Socket Cap Screws

Metric alloy flat head socket cap screws follow DIN 7991 (also referenced as ISO 10642), which governs dimensions, countersink angle, and mechanical requirements for metric countersunk hex socket fasteners. They are used in European-designed machinery, imported equipment, and any application where the design calls out metric hardware with a countersunk head. The 90° countersink angle is a critical specification — do not substitute inch-series (82°) fasteners without confirming that the countersunk holes have been reworked to match.

90° vs. 82° Countersink — Why It Matters

The 8° difference in countersink angle between metric (90°) and inch (82°) fasteners is enough to cause significant problems if mixed. An inch fastener in a 90° hole will sit proud of the surface with only the tip of the head contacting the hole — it will not pull flush and clamping force will be drastically reduced. A metric fastener in an 82° hole will over-seat at the tip, preventing it from drawing tight. Always match fastener and hole angle.

Specifications

Standard: DIN 7991 / ISO 10642
Property Class: Class 10.9 or Class 12.9 (Class 12.9 is standard for precision applications)
Tensile Strength: Class 12.9 — 1,220 MPa (~177,000 PSI); Class 10.9 — 1,040 MPa (~151,000 PSI)
Countersink Angle: 90° included
Drive: Internal hex (metric hex key sizes)
Size Range: M3 through M16 in stock; larger sizes available by request

Frequently Asked Questions

What standard covers metric flat head socket cap screws?
Metric flat head socket cap screws conform to DIN 7991 (German standard) and ISO 10642 (international standard). Both specify the same 90° countersink angle and metric hex socket drive. Class 12.9 is the standard alloy property class for precision machinery applications.

What is the countersink angle for metric flat head socket cap screws?
90° included angle per DIN 7991 / ISO 10642. This is different from inch-series flat head socket cap screws, which use an 82° angle per ASME B18.3. The two are not interchangeable — the mating countersunk hole must match the fastener angle.

What property class are metric alloy flat head socket cap screws?
Class 12.9 is standard, providing 1,220 MPa (~177,000 PSI) tensile strength. Class 10.9 (1,040 MPa) is also available and appropriate where slightly lower strength is acceptable. Specify Class 12.9 for precision machinery, tooling, and OEM applications.

Can I use metric flat head socket cap screws in a hole drilled for inch fasteners?
No. The 90° metric countersink angle does not match the 82° inch countersink angle. The fastener will not seat correctly, and clamping force will be significantly reduced. If you are transitioning from inch to metric hardware, the countersunk holes must be re-drilled and countersunk to 90°.

Metric alloy flat head socket cap screws are commonly used in assemblies alongside metric socket head cap screws, metric flat washers, and metric lock washers to maintain consistent thread standards throughout the design. For corrosive environments requiring metric countersunk fasteners, see metric stainless flat head socket cap screws. For inch-series countersunk applications, see alloy steel flat head socket cap screws (ASME B18.3, 82°). The full flat head socket cap screw selection is available through the Flat Head Socket Cap Screw category.

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