Flush-head flat and oval countersunk screws per DIN 7991 / ISO 10642 / ASME B18.6.3
Incoloy 925 countersunk screws (UNS N09925) are flush-head fasteners with a conical bearing surface under the head that sits inside a matching conical countersink in the joint, leaving the screw head flush (or sub-flush) with the joint surface. The 82° conical angle is standard for inch-series screws (ASME B18.6.3 para. 2.2.1, which also covers a 100° flat countersunk style, and ASME B18.3 para. 1.2.3 for socket flat countersunk head cap screws); 90° is standard for metric (DIN 7991 / ISO 10642). The flush-head configuration is essential where surface aerodynamics matter (aircraft skin panels), where the screw head must not protrude into a flow path (instrument fittings on smooth surfaces), or where aesthetic considerations demand a clean joint appearance. The conical bearing surface also provides positive self-centering as the screw is tightened. TorqBolt manufactures Incoloy 925 countersunk screws in M3 to M20 (#4 to 3/4") sizes per DIN 7991 / ISO 10642 (metric, internal hex drive) and ASME B18.6.3 (inch, slotted / cross-recessed) / ASME B18.3 (inch, hex socket), in the solution-annealed and aged condition with hardness controlled within the 38 HRC maximum that NACE MR0175 / ISO 15156-3 (Table A.32) sets for solution-annealed and aged N09925.
Need Incoloy 925 countersunk screws? Email info@torqbolt.com with diameter × length, head angle (82° / 90°), drive type (slotted / Phillips / Allen / hex), quantity. WhatsApp +91-22-66157017.
| Variant | Description | Standard |
|---|---|---|
| Flat-head countersunk (Allen drive) | 82° / 90° conical head with internal hex socket; flush installation | DIN 7991 / ISO 10642 / ASME B18.3 |
| Flat-head countersunk (Phillips / slotted) | Conical head with cross-recess (Phillips) or single-slot drive | ASME B18.6.3 / ISO 7046 |
| Oval-head countersunk (raised flush) | 82° conical bearing + slightly domed top surface | ASME B18.6.3 |
| Pan-head (round head, not flush) | Domed cylindrical head with flat bearing surface (NOT flush) | ASME B18.6.3 / ISO 7045 |
| 100° / 120° aerospace countersunk | Wider angle for thin-skin aerospace panels (NAS 1100 series) | NAS 1100 / 1101 / 1102 |
| Diameter | UNC | Metric Coarse | Head OD | Hex Socket | Length Range |
|---|---|---|---|---|---|
| #4 / M3 | UNC 40 | M3 × 0.5 | 5.5 mm | 2 mm | 5 to 40 mm |
| 1/4" / M6 | UNC 20 | M6 × 1.0 | 11 mm | 4 mm | 10 to 80 mm |
| 5/16" / M8 | UNC 18 | M8 × 1.25 | 14.5 mm | 5 mm | 12 to 100 mm |
| 3/8" / M10 | UNC 16 | M10 × 1.5 | 17.5 mm | 6 mm | 15 to 120 mm |
| 1/2" / M12 | UNC 13 | M12 × 1.75 | 21 mm | 8 mm | 20 to 150 mm |
| 5/8" / M16 | UNC 11 | M16 × 2.0 | 27 mm | 10 mm | 25 to 200 mm |
| 3/4" / M20 | UNC 10 | M20 × 2.5 | 33 mm | 12 mm | 30 to 250 mm |
Tensile 140 ksi (965 MPa) min / Yield 110 ksi (758 MPa) min, 140 ksi (965 MPa) max / Elongation 18% min / Hardness 26–38 HRC (API 6ACRA 110K; ISO 15156-3 Table A.32 caps solution-annealed and aged N09925 at 38 HRC) / Charpy V-notch at or below -60°C (-75°F): 35 ft-lb (47 J) average, 32 ft-lb (43 J) single min (API 6ACRA Table 6). See full mech properties page.
What's the difference between 82° and 90° head angle? 82° is the inch-series standard (ASME B18.6.3); 90° is the metric standard (DIN 7991 / ISO 10642). The angles are NOT interchangeable, an 82° screw in a 90° countersink (or vice versa) leaves the head proud or sub-flush and gives uneven bearing pressure on the conical surface. Specify the head angle to match the joint's countersink angle.
Can countersunk screws develop full preload? Not always. ISO 10642 designates hexagon socket countersunk head screws as having reduced loadability because of the head geometry combined with the socket depth (Clause 1, Note 2), and its Table 5 sets their minimum ultimate tensile loads at 80% of the ISO 898-1 / ISO 3506-1 values. The joint must also have a precision-machined matching conical countersink; ISO 10642 Clause 1, Note 3 calls for particular attention to seating the countersunk head on the countersink bearing surface. Imperfect countersinks cause concentrated stress and uneven preload. For high-preload applications, prefer machined countersinks over drilled / spot-faced ones.
Lead time? Standard sizes M5 to M16 / 1/4" to 5/8": 5–7 weeks. Larger / aerospace NAS variants: 8–10 weeks.
EN 10204 3.1 MTC (3.2 with TPI on request); chemistry, tensile, 100% hardness, head angle + drive recess inspection, thread Go/No-Go, NACE MR0175 reference. Related: socket head cap screws, hex cap screws, set screws, washers, full datasheet.
Email info@torqbolt.com · Phone +91-22-66157017 · WhatsApp +91-22-66157017. Specify variant, head angle (82° / 90° / aerospace), drive type, diameter × length, thread series, quantity, applicable standards (DIN 7991 / ISO 10642 / ASME B18.6.3 / NAS 1100), MTC level.
References: ASTM B805; DIN 7991 / 7046 / 7045; ISO 10642 / 7045 / 7046; ASME B18.6.3 / B18.3; NAS 1100 / 1101 / 1102; ASME B1.1 / B1.13M; NACE MR0175 / ISO 15156-3 Table A.32; EN 10204. INCOLOY® is a registered trademark of Special Metals Corporation.
