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 Lock Nuts
A286 lock nuts are non-prevailing-torque nuts that achieve anti-loosening through a secondary mechanical feature: jam nut (a second thinner nut tightened against the primary nut), pellet lock (nylon or metal pellet inserted in the side wall to friction-grip the bolt thread), slotted nut (radial slots for cotter-pin retention), or castle nut (slotted with raised crown). Distinguished from A286 self-locking nuts by the locking mechanism: lock nuts use external retainers (cotter pin, jam nut, pellet) while self-locking nuts use built-in prevailing torque (nylon insert or deformed thread). TorqBolt manufactures A286 lock nuts in M5-M64 metric and 1/4"-2-1/2" inch sizes — heat-treated to ASTM A453 grade 660 Class A from AMS 5731 hex bar. See parent A286 nuts, sister hex nuts, self-locking nuts, and the canonical chemical composition, mechanical properties.
About A286 Lock Nuts
A286 lock nuts come in four primary configurations: (1) Jam nut per DIN 936 / ISO 4035 — a thinner hex nut (~0.5 × nominal) used in pairs against a standard hex nut to friction-lock; the assembly is the canonical "double-nut" anti-vibration design. (2) Pellet lock nut — standard hex nut with a nylon or aluminium pellet inserted in a side-wall pocket, friction-engaging the bolt thread without prevailing torque on the primary nut. (3) Slotted nut per DIN 935 / ISO 7037 — six radial slots for cotter-pin retention through a transverse hole in the bolt shank. (4) Castle nut per ASME B18.2.2 — slotted with raised crown, similar function to slotted but with extra height. Each is upset-forged from A286 hex bar, tapped, then solution-treated 1650 °F + aged 1325 °F per AMS 5737.
A286 Lock Nut Types & Standards
TorqBolt produces five primary A286 lock nut configurations:
- Jam nut (DIN 936 / ISO 4035) — Thinner hex nut (~0.5 × nominal) used in pairs against a standard hex nut. Bottom nut takes the load; top jam nut provides friction-lock against the bottom nut. M5-M64 sizes.
- Pellet lock nut (custom / IFI-100D) — Standard hex nut with nylon (low-temp) or aluminium (high-temp) pellet in a side-wall pocket — friction engages bolt thread on assembly. Re-usable 8-10 cycles.
- Slotted nut (DIN 935 / ISO 7037) — Hex nut with 6 radial slots cut across the top — cotter pin passes through transverse hole in bolt shank and engages a slot. Positive lock against rotation.
- Castle nut (ASME B18.2.2) — Hex nut with raised crown above the slotted section — taller than slotted nut, used where extra cotter-pin clearance is needed. Common on automotive wheel-bearing retention.
- Heavy hex jam nut (ASME B18.2.2 thin) — Thinner heavy hex nut for use in pairs on ASME B16.5 flange bolting where prevailing torque is required at temperatures above 120 °C nylon limit.
A286 Lock Nut Sizes & Reference
| Metric size | Wrench AF | Standard hex thickness | DIN 936 jam thickness | DIN 935 slotted thickness | Castle nut thickness |
|---|---|---|---|---|---|
| M6 | 10 mm | 5 mm | 3 mm | 7.5 mm | 10 mm |
| M8 | 13 mm | 6.5 mm | 4 mm | 9.5 mm | 13 mm |
| M10 | 17 mm | 8 mm | 5 mm | 12 mm | 16 mm |
| M12 | 19 mm | 10 mm | 6 mm | 15 mm | 19 mm |
| M16 | 24 mm | 13 mm | 8 mm | 19 mm | 23 mm |
| M20 | 30 mm | 16 mm | 9.5 mm | 22 mm | 29 mm |
| M24 | 36 mm | 19 mm | 12 mm | 27 mm | 33 mm |
| M30 | 46 mm | 24 mm | 15 mm | 33 mm | 40 mm |
A286 Lock Nuts Manufacturing Process
Every a286 lock 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:
- Bar prep + upsetting: AMS 5731 hex bar drawn to nut OD. Hot-upset blank with bevelled top + bottom + central pilot hole. Jam nuts use thinner blank.
- Slot machining (slotted / castle): Six radial slots milled in top portion of nut blank. Castle nut adds raised crown — turning + boring operation.
- Tapping: Internal thread tapped per ISO 1502 6H (commercial) or MIL-S-8879 (aerospace) on automatic tapping line.
- Solution treatment: Vacuum heat-treat 1650 °F (899 °C) per AMS 5737 / ASTM A453 Class A.
- Precipitation aging: 1325 °F (718 °C) for 16 hours, air-cool. Hardness 24-32 HRC post-aging.
- Pellet pocket drilling (pellet lock): Side-wall pocket drilled and pellet pressed in for pellet-lock variant.
- Passivation: Pickle + HNO₃ rinse + passivate per ASTM A967 Type II.
- Marking + pack: Stamped 'A286' + lot + manufacturer 'TB'. Bulk pack 100 / 250 / 500 pcs.
- Inspection + test: 100 % thread gauge; jam-nut variant tested for proper fit on master nut; slotted/castle inspection of slot dimensions.
A286 Lock Nuts Inspection & Certification
Each lot ships with a signed inspection certificate. Aerospace lots default to AS9102 FAI reporting under our AS9100D AQMS coverage. Industrial orders default to EN 10204 type 3.1. Variant-specific inspection scope:
- 100 % thread plug gauge per ISO 1502 6H (commercial) or MIL-S-8879 (aerospace).
- Wrench across-flats verified by snap gauge.
- Slot dimension verified on slotted/castle variants — slot width and depth per DIN 935.
- Pellet pocket dimension and pellet retention force tested on pellet-lock variants (1 per 100).
- Hardness traverse 4-point Vickers per heat-treat batch.
- Magnetic permeability < 1.005 per ASTM A342 on every aerospace coil.
- AS9102 first-article on aerospace lots; EN 10204 3.1 commercial.
- Salt-spray ASTM B117 96-hour for passivated lots.
A286 Lock Nuts Torque & Assembly Practice
Lock nut torque depends on the locking mechanism: (1) Jam-nut pair — bottom nut torqued to full preload (75 % yield), top jam nut torqued to 50-60 % of bottom nut's torque. (2) Pellet lock — torqued to full preload; pellet provides friction without affecting seating torque. (3) Slotted / castle — torqued to specified preload, then loosened to align next slot with cotter-pin hole (NEVER tightened beyond preload to align). Cotter pin provides positive lock; preload is set by initial torque only. Above 540 °C apply nickel anti-seize to threads on all variants.
A286 Lock Nut Applications by Industry
Lock nuts retain primary nut against loosening — applications:
- Static bolted joints with vibration risk: DIN 936 jam-nut pairs on petrochemical heat-exchanger bolting, oil-pump flange connections — high-temperature alternative to nylon-insert.
- Aerospace control-linkage: Slotted nuts (DIN 935) on flight-control linkage clevis pins, hinge points — cotter pin provides positive rotational lock. Used where MS 21043 self-locking is unsuitable.
- Automotive wheel bearing: Castle nuts (ASME B18.2.2) on car / truck axle nuts, bearing-housing retention — positive cotter-pin lock against rotation.
- Industrial gas turbines: DIN 936 jam-nut pairs on combustor liner shell bolting where service exceeds 120 °C nylon limit. A286 gas turbine applications.
- Defence airframe: Castle and slotted nuts on F-16 / F-22 landing gear, control-surface hinges — positive cotter-pin lock for safety-critical joints.
- Marine / offshore: Pellet-lock nuts on subsea connector body retention — corrosion-resistant + vibration-resistant + non-prevailing-torque (avoids gripping issue at depth).
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. See the consolidated A286 AMS / ASTM specifications hub.
| 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 — sol-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 |
A286 Lock Nuts vs Alternative Materials
Engineers compare A286 against three alternatives: A286 vs Inconel 718, A286 vs 17-4 PH, and A286 vs Waspaloy. Within the 540-700 °C service envelope A286 is the dominant cost-performance choice for non-magnetic, oxidation-resistant bolting. See A286 equivalent grades.
How to Specify A286 Lock Nuts
A complete a286 lock nuts callout should include all eight elements: material spec, heat-treatment condition, dimensional standard, size, thread tolerance class, surface finish, marking, inspection certificate. Example callout:
Hex jam nut, DIN 936 (ISO 4035), A286 / UNS S66286, ASTM A453 grade 660 Class A, ST+A, M16 × 2.0, 6H thread, passivated, stamped ‘A286’ + lot, EN 10204 3.1.
A286 Lock Nuts — Frequently Asked Questions
What is the difference between a lock nut and a self-locking nut?
Lock nut uses an external retainer (cotter pin, jam nut, pellet) to prevent rotation. Self-locking nut has built-in prevailing torque (nylon insert or deformed thread). Lock nuts are typically more re-usable and higher-temperature; self-locking nuts are simpler to install and more compact.
How do I install a jam-nut pair?
Thread the standard (full-thickness) nut to position and torque to full preload (75 % yield). Then thread the jam-nut (DIN 936 thin nut) on top and tighten against the standard nut at 50-60 % of the standard's torque. The jam-nut friction-locks against the standard nut, preventing both from rotating.
Can A286 lock nuts be re-used?
Jam nuts: indefinitely re-usable. Pellet-lock nuts: 8-10 cycles per IFI-100D before pellet wears. Slotted/castle nuts: indefinitely re-usable but cotter pin must be replaced each cycle. Aerospace primary structure: single-use only per OEM SRM.
Can A286 lock nuts be used at high temperature?
DIN 936 jam nuts: yes to 700 °C (full A286 service temp). Pellet-lock with nylon pellet: ≤ 120 °C; with aluminium pellet: ≤ 540 °C. Slotted/castle: yes to 700 °C. Choose pellet material per service temp.
What's the difference between a slotted nut and a castle nut?
Slotted nut (DIN 935): hex nut with 6 radial slots cut across the top — slot depth ~0.6 × hex thickness. Castle nut (ASME B18.2.2): slotted with raised crown above the slot section — overall taller. Same function (cotter-pin retention) but castle nut allows more cotter-pin clearance.
Are A286 lock nuts magnetic?
No. Magnetic permeability < 1.005 verified on every aerospace lot per ASTM A342.
What torque for an A286 jam-nut pair?
Bottom nut: 75 % of bolt yield (full preload). Top jam nut: 50-60 % of bottom's torque. For M16 grade 660 Class A: bottom 280 N·m, jam 150-170 N·m. Always tighten in this order — bottom first to develop preload, then jam-nut to lock.
Why use a slotted nut instead of a self-locking nut?
Positive mechanical lock from cotter pin — no reliance on friction (which can vary or fail). Used on safety-critical joints where the consequences of loosening are catastrophic: landing gear, control linkages, primary structure. Slotted requires drilled bolt shank for cotter pin.
What size cotter pin for an M10 slotted nut?
Cotter pin diameter ≈ 0.2 × bolt nominal: M10 → 2 mm cotter pin (1/16 inch typical). Length ≈ 1.5 × bolt diameter past the nut. ASME B18.8.2 / DIN 94 covers cotter pin sizing.
Why TorqBolt for A286 Lock Nuts
Three reasons aerospace and gas-turbine OEMs place a286 lock nuts orders with us:
- Vertically integrated supply — VIM-VAR melt, in-house cold heading + thread rolling + vacuum heat-treatment.
- Aerospace AQMS — AS9100D-certified factory in Mumbai with published quality manual.
- Lead time discipline — 4-6 weeks standard, 8-12 weeks aerospace custom.
30+ years of fastener-manufacturing track record. Active certifications cover ISO 9001:2015, AS9100D AQMS, PED 2014/68/EU and NORSOK M-650 QTR.
Recent A286 Lock Nuts Order Patterns
Recurring lock-nut orders: DIN 936 jam-nut pairs on petrochemical heat-exchanger flange bolting, DIN 935 slotted on aerospace flight-control linkages, ASME B18.2.2 castle nut on heavy-truck axle and bearing-housing retention, and pellet-lock variants on subsea connector bodies.
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