Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
A286 Hex Nuts
A286 hex nuts are the canonical mating fastener for A286 hex bolts, A286 bolts and A286 stud bolts. Manufactured by TorqBolt to DIN 934, ISO 4032 (Type 1 standard), ISO 4033 (Type 2 heavy), and ASME B18.2.2 dimensional standards in M5-M64 metric and 1/4"-2-1/2" inch series. Each A286 hex nut is upset-forged from A286 hex bar (AMS 5731 / 5736), tapped, then solution-treated and precipitation-aged to develop the full Class 8 mechanical strength. Pair with A286 hex bolts to form a fully matched A286 bolted joint that retains preload to 700 °C — see parent A286 nuts overview, sister variants self-locking nuts, lock nuts, and the canonical A286 mechanical properties, chemical composition, heat treatment pages.
About A286 Hex Nuts
TorqBolt produces Alloy A286 (UNS S66286) hex nuts in three thickness types: Type 0 thin (~0.5d, ISO 4035), Type 1 standard (~0.8d, ISO 4032 / DIN 934 — the default), and Type 2 heavy (~0.9d, ISO 4033 / DIN 6330). All are six-flat external hex with internal threaded hole, hot-upset from A286 hex bar (AMS 5731), thread-tapped, solution-treated 1650 °F (899 °C), and aged 1325 °F (718 °C) for 16 hours. Hardness 24-37 HRC, proof load 130 ksi (895 MPa), guaranteed at -196 °C and 700 °C. The non-magnetic austenitic matrix (permeability ≈ 1.001) makes A286 hex nuts compatible with the same instrumentation, MRI, electronic and aerospace electromagnetic-sensitive joints as A286 hex bolts.
A286 Hex Nut Types & Dimensional Standards
Three primary hex nut profiles are produced:
- Type 1 standard hex nut (ISO 4032 / DIN 934) — Standard thickness ≈ 0.8 × nominal diameter. The default for general bolted-joint pairing. Wrench across-flats matches DIN 931 / 933 hex bolt heads.
- Type 2 heavy hex nut (ISO 4033 / DIN 6330 / ASME B18.2.2) — Thicker (≈ 0.9d) for high-load and structural applications. Used on stud-bolted flange joints per ASME B16.5 and high-temperature bolting per ASTM A453.
- Hex thin / jam nut (ISO 4035 / DIN 936) — Reduced thickness (~0.5d) — used as a locking jam nut in pairs or on low-clearance shoulder applications. Lower load capacity — not for primary load.
- Hex flange nut (DIN 6923 / IFI-100) — Integral flange spreads bearing pressure — eliminates separate washer. Common on automotive turbocharger bolting.
- Hex slotted nut (DIN 935 / ISO 7037) — Six radial slots for cotter-pin retention — used on rotating-shaft applications where positive lock against unscrewing is required.
A286 Hex Nut Sizes & Wrench Reference
| Metric size | Pitch (coarse) | Wrench AF | Standard thickness | Heavy thickness | Proof load (kN) |
|---|---|---|---|---|---|
| M6 | 1.0 | 10 mm | 5 mm | 5.5 mm | 20.0 |
| M8 | 1.25 | 13 mm | 6.5 mm | 7.5 mm | 36.4 |
| M10 | 1.5 | 17 mm | 8 mm | 9.5 mm | 57.8 |
| M12 | 1.75 | 19 mm | 10 mm | 12 mm | 84.0 |
| M16 | 2.0 | 24 mm | 13 mm | 16 mm | 157 |
| M20 | 2.5 | 30 mm | 16 mm | 19 mm | 244 |
| M24 | 3.0 | 36 mm | 19 mm | 22 mm | 353 |
| M30 | 3.5 | 46 mm | 24 mm | 27.5 mm | 560 |
A286 Hex Nuts Manufacturing Process
Every a286 hex nuts TorqBolt ships traces back to a vacuum-induction-melted plus vacuum-arc-remelted (VIM-VAR) ingot meeting AMS 5731 / 5732 chemistry. The complete process route is variant-specific:
- A286 hex bar input: Hex-cross-section A286 bar (AMS 5731) drawn to nut OD. Bar across-flats matches finished nut wrench size: M6 nut → 10 mm AF hex bar, M10 → 17 mm, M16 → 24 mm, M24 → 36 mm.
- Hot upsetting (Type 1 standard): Hex bar cut to slug, heated to 1050 °C, upset in a hex die-press to form bevelled top + bottom + central pilot hole. Single-station for M5-M16, multi-station for M20-M64.
- Cold extrusion (sizes ≤ M12): For high-volume Type 1 standard nuts, cold-extruded direct from bar via 3-station progressive press: pilot → upset → flash trim.
- Tapping: Internal thread tapped on automatic tapping line — Class 6H metric, 2B / 3B inch. Aerospace nuts use MIL-S-8879 thread tolerance.
- Solution treatment: Vacuum heat-treat 1650 °F (899 °C, AMS 5737) or 1800 °F (982 °C, AMS 5732) for 1 h per inch, oil-quench.
- Precipitation aging: Re-heat 1325 °F (718 °C) for 16 hours, air-cool. Aging causes 0.05 % thread shrinkage — re-tap to spec post-aging if MIL precision required.
- Surface finish: Pickle / passivate per ASTM A967 type II. For high-temperature service apply silver or nickel anti-galling coat per AS5272 to inner thread bore.
- Lot inspection: 100 % thread gauge GO/NO-GO; hardness traverse 4-point Vickers per heat-treat batch; magnetic permeability check on every coil; LPI on aerospace lots.
- Marking: Stamped on one face: 'A286' + lot + manufacturer 'TB' per ASTM F812. Larger nuts also stamp grade marking 'GR 660' for ASTM A453 traceability.
A286 Hex Nuts Inspection & Certification
Each lot ships with a signed inspection certificate. Aerospace orders default to AS9100D first-article reporting per AS9102 on the first part of any new drawing or revision. Industrial orders default to EN 10204 type 3.1; sour-service and offshore orders step up to type 3.2 with third-party witness present at heat-treat release and tensile testing. Variant-specific inspection scope:
- 100 % thread plug gauge per ANSI/ASME B1.1 (inch) or ISO 1502 (metric) — full assembly with master bolt verifies start, run-down, and seating.
- Across-flats wrench dimension verified by snap-gauge — tolerance per DIN 934 / ISO 4032 (typ. ±0.30 mm at M16).
- Across-corners dimension verified by go/no-go gauge — confirms hex geometry for socket-wrench engagement.
- Hardness traverse 4-point Vickers per heat-treat batch (3 corners + 1 face).
- Tensile coupon from each heat — proof-load test on assembled bolt+nut combination per ASTM F606.
- Magnetic permeability < 1.005 per ASTM A342 on every aerospace lot.
- AS9102 first-article inspection on aerospace nuts per AS9100D AQMS.
- Salt-spray test 96-hour pass per ASTM B117 / A967 when passivation invoked.
TorqBolt’s quality file maintains the audited NORSOK M-650 QTR for A286 fastener manufacture, renewed every 5 years. Customer-witnessed source surveillance is welcomed.
A286 Hex Nuts Torque & Assembly Practice
A286 hex nuts torque to the same proof-load as their mating A286 hex bolts — the nut-to-bolt match is critical to avoid over-stressing the weaker member. ASTM F606 prescribes proof-load testing the assembled joint: nut applied to a high-strength threaded mandrel + tightened to specified proof load + held for 15 seconds without thread strip. For the M16 grade-660 Class A combination: proof load 157 kN (35,300 lbf), torque-to-yield 280 N·m oil / 180 N·m anti-seize. Heavy hex (Type 2) does NOT increase proof load (limited by bolt strength), but provides higher bearing area on softer mating surface. Above 540 °C apply nickel anti-seize to inner thread bore — austenitic-stainless threads gall above this temperature.
A286 Hex Nut Applications by Industry
Hex nuts pair with hex bolts and stud bolts to complete the bolted joint. Industry uses:
- Aerospace engine bolting: Standard mate for NAS 6603-6620 hex bolts on jet-engine compressor and turbine assemblies. Heavy hex preferred for high-preload disc-to-disc bolting. A286 jet engine fasteners.
- Industrial gas turbines: Casing-split flange nuts, combustor liner retention nuts, exhaust diffuser bolting. A286 gas turbine applications.
- Petrochemical flange bolting: ASME B16.5 raised-face flange joints with stud bolts + heavy hex nuts. ASTM A453 grade 660 Class A or B per service temperature.
- Oil & gas downhole: Subsea connector body retention. NACE MR0175 hardness limit ≤ HRC 35 verified per heat.
- Cryogenic LNG: Valve-bonnet flange nuts, cryogenic pump bolting. A286 hex nuts retain 85 % of RT toughness at -196 °C.
- Nuclear: ASME III subsection NB hex nuts on pressuriser, steam-generator, and primary-coolant pump bolting. A286 nuclear applications.
Governing Standards & Material Specifications
Every A286 fastener is released against the applicable industry standard. EN 10204 type 3.1 mill certificates ship with every order; type 3.2 third-party-witnessed inspection is available for nuclear, offshore and customer-mandated source-surveillance contracts. See the consolidated A286 AMS / ASTM specifications hub for full spec scope.
| Authority | Specification | Coverage |
|---|---|---|
| ASTM | A453 grade 660 Cl. A/B/C/D | High-temperature bolting material |
| ASTM | A638 grade 660 Type 1/2 | Forged bolting stock |
| AMS | 5731 | Bar / forging — solution-treated |
| AMS | 5732 | Bar / forging — solution-treated and aged |
| AMS | 5737 | Bar — solution-treated and aged (precision) |
| UNS | S66286 | Material designation |
| DIN | 1.4980 / X5NiCrTiMoVB25-15-2 | European designation |
| EN | 10204 3.1 / 3.2 | Mill / third-party-witness certification |
| NACE | MR0175 / ISO 15156-3 | Sour-service hardness limit ≤ HRC 35 |
A286 Hex Nuts vs Alternative Materials
When selecting a fastener material engineers compare A286 against three alternatives: A286 vs Inconel 718 (top-end performance, 3× cost), A286 vs 17-4 PH (cheaper but limited to 315 °C), and A286 vs Waspaloy (sustained service > 700 °C). A286 is the cost-performance leader for non-magnetic precipitation-hardening service in the 540-700 °C envelope. See the consolidated A286 equivalent grades reference for full alloy alternatives.
How to Specify A286 Hex Nuts
A complete a286 hex nuts callout on a drawing or purchase order should include all eight elements: material spec, heat-treatment condition, dimensional standard, size, thread tolerance class, surface finish, marking, inspection certificate. Example complete callout:
Hex nut, ASTM A453 grade 660 Class A, ST+A, DIN 934 Type 1 standard, M16 × 2.0, 6H, passivated, stamped ‘A286’ + lot, EN 10204 3.1.
A286 Hex Nuts — Frequently Asked Questions
What is the difference between Type 1 and Type 2 A286 hex nuts?
Type 1 (standard, ISO 4032 / DIN 934) thickness ≈ 0.8 × nominal diameter. Type 2 (heavy, ISO 4033 / ASME B18.2.2) thickness ≈ 0.9 × nominal — gives higher bearing area. Use Type 2 for ASME flange bolting, structural connections, and high-temperature joints.
Can A286 hex nuts mate with stainless steel A2 / A4 bolts?
Mechanically yes, but galling is a concern: austenitic-stainless on austenitic-stainless threads gall above 540 °C. Apply nickel or copper anti-seize, or use a different alloy mating combination. For aerospace-critical joints, match A286 nuts to A286 bolts only.
What is the proof load of an M16 A286 hex nut?
157 kN (35,300 lbf) for ASTM A453 grade 660 Class A material — equal to the proof load of the mating M16 A286 hex bolt at 130 ksi proof stress on M16 stress area 157 mm². Heavy hex Type 2 has the same proof load — the difference is bearing area, not strength.
Are A286 hex nuts magnetic?
No. A286 austenitic matrix has magnetic permeability ≈ 1.001 — essentially non-magnetic. This is preserved through cold work and aging, making A286 hex nuts compatible with MRI, mass spectrometer, magnetometer, and electromagnetic-sensitive aerospace assemblies.
What is the difference between hex nut and hex flange nut?
Hex flange nut has an integral flange that spreads bearing pressure under the nut — eliminates the need for a separate flat washer. Standard hex nut requires a separate A286 flat washer. Hex flange nuts (DIN 6923) are common on automotive and exhaust-system applications.
Can A286 hex nuts be used with anti-vibration features?
Yes — TorqBolt produces A286 self-locking nuts (nylon insert per DIN 985 or all-metal prevailing-torque per IFI-100) and A286 lock nuts (jam-nut and pellet-lock variants). Choose self-locking for cycling joints, jam nuts for static joints with vibration risk.
How is an A286 hex nut tested for proof load?
ASTM F606 procedure: nut threaded onto a hardened steel mandrel of specified strength, tightened to proof load (130 ksi for grade 660 Class A), held 15 seconds, then removed. Pass criterion: no thread strip, no visible yielding of nut. Each lot is sampled at 1 nut per 1000.
What hardness should an A286 hex nut be?
24-37 HRC after solution-treatment + aging per ASTM A453 grade 660. Nuts are intentionally aged to slightly lower hardness than mating bolts (32-37 HRC bolt vs 24-30 HRC nut) so that yield distributes across nut threads, not bolt threads — the 'sacrificial nut' design principle.
Are A286 hex nuts NACE MR0175 compliant?
Yes when hardness verified ≤ HRC 35. TorqBolt aging schedules for sour-service nuts target the upper end of the hardness range (32-34 HRC) to balance NACE compliance with adequate proof load. Each heat receives a Vickers traverse before release.
Why TorqBolt for A286 Hex Nuts
Three reasons aerospace and gas-turbine OEMs place a286 hex nuts orders with us:
- Vertically integrated supply — VIM-VAR melt sourcing from approved AMS-conforming mills, in-house cold heading + thread rolling + vacuum heat-treatment. No outsourced critical step.
- Aerospace AQMS — AS9100D-certified factory in Mumbai with a published quality manual covering A286 fastener-specific failure-mode analysis (preload retention, hydrogen embrittlement, thread fatigue, galling).
- Lead time discipline — 4-6 weeks for ASTM A453 grade 660 standard sizes, 8-12 weeks for custom-drawing aerospace parts. No surprises.
30+ years in fastener manufacture; no MOQ on stocked DIN / ISO patterns; ISO 9001:2015 + AS9100D + PED 2014/68/EU + NORSOK M-650 QTR all current. Lot traceability runs from VIM-VAR melt heat number through finished-part packaging.
Recent A286 Hex Nuts Order Patterns
Recurring hex-nut order categories: petrochemical refinery flange bolting (M24 heavy hex), aerospace engine matched-pair lots (NAS 1291-style bolt + nut), gas-turbine casing-split bolting (M30), and oilfield downhole-tool body retention (1-inch UNF NACE-verified). Matched-pair bolt + nut traceability is the recurring requirement.
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