Alloy Flat Head Socket Cap Screws

Alloy steel flat head socket cap screws (inch series) are heat-treated countersunk fasteners conforming to ASTM A574 and ASME B18.3. The 82° countersunk head sits flush with or below the workpiece surface, and the internal hex drive handles significantly higher installation torque than Phillips or slotted drivers of comparable size. With a minimum tensile strength of 170,000 PSI in sizes through 1/2", alloy flat head socket cap screws deliver both flush installation and the clamping force required for structural and tooling applications. Eugene Fastener stocks a full inch size range from stock in Eugene, Oregon.

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Alloy Steel Flat Head Socket Cap Screws — Inch Series, ASTM A574

Shop Alloy Flat Head Socket Cap Screws

Alloy steel flat head socket cap screws are the workhorse of countersunk socket fasteners. Heat treated to ASTM A574, they provide 170,000 PSI minimum tensile strength for sizes #0 through 1/2", and 180,000 PSI for sizes 5/8" and larger — making them the strongest commercially available countersunk socket fastener in standard production. The 82° included angle (ASME B18.3) matches standard inch-series countersink tooling. A hex key (Allen wrench) drives the fastener to full torque from within the counterbored recess.

Specifications

Standard: ASME B18.3 (dimensional) / ASTM A574 (mechanical)
Tensile Strength: 170,000 PSI min. (#0 through 1/2"); 180,000 PSI min. (5/8" and larger)
Hardness: RC 37–45
Countersink Angle: 82° included
Drive: Internal hex (Allen key / hex socket)
Finish: Plain (bright) or black oxide
Material: Alloy steel, heat treated

Size Range

Inch alloy flat head socket cap screws are available in thread sizes from #0-80 through 1"-8, with lengths from 1/8" through 4" and longer depending on diameter. Common stock sizes run from #4-40 through 1/2"-13 in the most frequently used lengths. Contact us for sizes outside standard stocking range.

Finish Options

Plain (bright) finish is standard — bare alloy steel with a light oil coating for corrosion protection during storage. Black oxide finish provides a matte appearance and mild corrosion resistance for indoor applications. Neither finish is suitable for outdoor or wet environments; for corrosion resistance, see our stainless steel flat head socket cap screws.

Common Applications

Alloy flat head socket cap screws are used in tooling plates and fixture bases where a protruding head would interfere with workpiece seating, machine guards and panel assemblies requiring flush fastener surfaces, OEM machinery and equipment enclosures, and precision mechanical assemblies where countersinking maintains part alignment and clearances.

Frequently Asked Questions

What grade are alloy flat head socket cap screws?
Alloy flat head socket cap screws conform to ASTM A574, which specifies mechanical requirements including minimum tensile strength of 170,000 PSI (sizes through 1/2") and 180,000 PSI (sizes 5/8" and larger). This exceeds SAE Grade 8 hex bolts (150,000 PSI).

What is the countersink angle for alloy flat head socket cap screws?
82° included angle per ASME B18.3, which is the standard for all inch-series flat head socket cap screws. Metric flat head socket cap screws use a different 90° angle — the two are not interchangeable. Confirm your countersink tooling angle before ordering.

What finish is standard on alloy flat head socket cap screws?
Plain (bright) finish is most common — bare alloy steel with light oil. Black oxide is available in most sizes and provides a uniform matte appearance with minimal corrosion protection. For wet or outdoor environments, use stainless steel flat head socket cap screws instead.

What tensile strength do alloy flat head socket cap screws have?
170,000 PSI minimum for sizes #0 through 1/2". 180,000 PSI minimum for sizes 5/8" and larger. Both exceed Grade 8 hex bolt requirements and make alloy FHSCS the highest-strength standard countersunk socket fastener available.

Alloy flat head socket cap screws are commonly paired with flat washers and lock washers in through-hole assemblies, and with socket head cap screws in mixed assemblies where some positions require flush seating and others do not. For corrosive environments, see stainless steel flat head socket cap screws. For metric countersunk applications, see metric alloy flat head socket cap screws (DIN 7991, 90° angle). The full flat head socket cap screw selection — alloy, stainless, inch, and metric — is available through the Flat Head Socket Cap Screw category.

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