Standards
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175 / ISO 15156-2
- NORSOK M-650 Qualified
- API 6A Certified
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Incoloy 925 Countersunk Screws (UNS N09925)
Flush-head flat / oval / pan 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); 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 / Phillips / hex drive variants), in the solution-annealed and aged condition with hardness controlled within the 35 HRC NACE MR0175 sour-service cap.
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.
Countersunk Screw Variants
| 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 |
Standard Size Range
| 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 |
Mechanical Properties (Aged)
Tensile 165 ksi min / Yield 110 ksi min / Elongation 18% min / Hardness 32–35 HRC (NACE cap) / Charpy at -46°C: 40 J min. See full mech properties page.
Applications
- Sour-service instrument enclosures (flush-head appearance + corrosion resistance)
- Subsea control-pod covers (flush mounting in chloride seawater)
- Aerospace skin-panel attachment (NAS 1100-series 100° aerospace countersunk)
- Architectural / decorative joint fastening (where head profile must be flush)
- Hydraulic manifold port plugs (countersunk + sealing washer)
- Marine deck-plate fastening (where flush head prevents tripping hazard)
- Flow-path internal bolts (smooth surface to minimize disturbance)
Standards
- ASTM B805, UNS N09925 forging stock
- DIN 7991, Hexagon Socket Countersunk Head Screws (metric, 90° head)
- ISO 10642, Hexagon Socket Countersunk Head Screws (metric)
- ISO 7046, Phillips-recess countersunk machine screws
- ASME B18.6.3, Machine Screws and Machine Screw Nuts (inch, 82° head)
- NAS 1100 / 1101 / 1102, Aerospace countersunk screws (100°, 130° variants)
- ASME B1.1 / B1.13M, thread series; NACE MR0175 Table A.10; EN 10204 3.1 / 3.2
Manufacturing Sequence
- Bar input per ASTM B805 in annealed condition
- Cold-upset conical head with integral hex socket / Phillips recess / slotted feature
- Head bearing-surface finishing (precision conical angle, surface finish per DIN 7991 / ISO 10642)
- Shank machining + thread rolling (annealed condition)
- Solution anneal + age cycle per heat-treatment specification
- Final inspection: head angle + diameter, drive recess Go / No-Go, thread Go / No-Go, 100% hardness
- Marking: heat number on head face (or bagged for small sizes) + grade designation + NACE stamp
Frequently Asked Questions
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? Yes, the conical bearing surface develops the same axial preload as a flat-head fastener, but the joint must have a precision-machined matching conical countersink. 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.
Documentation Package & Related Products
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.
Request a Quote
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.10; EN 10204. INCOLOY® is a registered trademark of Special Metals Corporation.
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