Flat Head Cap Screws

Flat head socket cap screws combine a countersunk head with an internal hex drive, seating flush with the work surface for a clean, snag-free finish. The conical bearing surface centers the screw and distributes load, while the socket drive delivers high torque in a low-profile package. They are standard in machine tools, dies, fixtures, and any assembly requiring a flush, high-strength fastener.

Why Flat Head Socket Cap Screws

The countersunk head sits flush or below the surface, eliminating protrusions that could interfere with moving parts or mating components. The internal hex drive provides far more torque capacity than a slotted or Phillips flat head, making these screws the high-strength choice for flush mounting in metal.

Head Angle

Inch flat head socket cap screws use an 82-degree countersink; metric versions use 90 degrees. The head angle must match the countersink in the workpiece—mismatched angles concentrate stress on a thin contact ring and can crack the head or pull through. Always verify your countersink tool matches the screw standard.

Grades and Materials

Alloy steel, Class 12.9: the standard—through-hardened to roughly 170 ksi tensile, typically black oxide finished. 18-8 stainless: corrosion resistance for general use. 316 stainless: marine and chemical environments. Stainless versions trade peak strength for corrosion resistance.

Dimensional Standards

Inch flat head socket cap screws conform to ASME B18.3 (82°). Metric versions follow DIN 7991 / ISO 10642 (90°). Both use an internal hex drive sized to the screw.

Selecting the Right Flat Head Socket Cap Screw

Confirm the head angle matches your countersink (82° inch, 90° metric). Choose Class 12.9 alloy for maximum strength or stainless for corrosion resistance. Size the countersink so the head finishes flush—too shallow leaves the head proud, too deep reduces bearing area. Verify thread pitch matches the tapped hole and select the correct hex key for installation.

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