Monel 400
Nuts
UNS N04400
Monel 400 Nuts — Matched Assembly Principle
Monel 400 (UNS N04400) is an annealed nickel-copper alloy — 63–70% Ni, copper balance — delivering permanent seawater and HF acid immunity in bolted assemblies. When a Monel 400 stud bolt contacts a 316L nut in seawater, the dissimilar metals form a galvanic couple in the chloride electrolyte: 316L is anodic to Monel 400 and corrodes preferentially at the thread-nut interface, causing crevice attack, thread seizure, and loss of clamping load within months.
Using matched UNS N04400 Monel 400 nuts eliminates this failure path. Same alloy throughout — zero potential difference, no galvanic cell, no accelerated corrosion at the thread interface in permanent seawater immersion, splash zones, or HF acid exposure. Akbar Fasteners Pvt. Ltd. supplies Monel 400 nuts from the same ASTM B164 certified heat as the matching stud bolts and bolts — one mill test certificate covers the complete assembly, simplifying QC documentation for third-party inspectors and NACE auditors.
For assemblies requiring ≥1000 MPa bolt loads, step up to our Monel K500 nuts in age-hardened UNS N05500. For reducing acid service where Monel 400 is insufficient, our Hastelloy B3 matched nut sets are available alongside B3 stud bolts.
| Element | Min % | Max % | Typical |
|---|---|---|---|
| Nickel + Cobalt | 63.0 | — | ~67% |
| Copper (Cu) | — | Balance | ~31% |
| Iron (Fe) | — | 2.5 | ~1.5% |
| Manganese (Mn) | — | 2.0 | ~1.0% |
| Carbon (C) | — | 0.30 | <0.15% |
| Silicon (Si) | — | 0.50 | <0.3% |
| Sulfur (S) | — | 0.024 | — |
Monel 400 Nut Types & Standards
All types machined from ASTM B164 certified UNS N04400 annealed bar. PMI-verified before production. Full MTC and COC on every order.
Standard Hex Nuts
The most common Monel 400 nut type. DIN 934 dimensions — six equal flat sides, standard height — for Monel 400 hex bolt and threaded rod assemblies in seawater pump flanges, marine hardware, and HF acid piping. Metric DIN 13 or inch UNC/UNF thread. M6–M100.
Heavy Hex Nuts
Wider across-flats and taller than DIN 934 — mandatory for ASME B16.5 stud bolt assemblies in Class 150–2500 pressure flanges. Greater bearing area and longer thread engagement. M12–M100. Supplied as certified sets with matching Monel 400 stud bolts from same heat on request.
Coupling Nuts
Extended-length hex nuts (typically 3× bolt diameter) for joining two threaded rods or connecting a stud to a threaded rod in marine hanger systems. Used with Monel 400 threaded rods in offshore platform equipment supports and seawater pipe bracket systems. M6–M48.
Slotted, Flanged & Custom
Slotted (castle) nuts for pin-retention in marine propeller shaft assemblies, flanged hex nuts for soft GRP substrates, and non-standard across-flats. Left-hand thread available. Send drawing to sales@akbarfasteners.in.
Inch Thread Hex Nuts
Standard and heavy hex nuts in UNC (¼”–4″) and UNF thread per ASME B18.2.2 inch dimensions for US naval, offshore, and export projects specified in imperial. Same ASTM B164 certified UNS N04400 annealed material. Full MTC and PMI.
Stud Bolt + Nut Sets
Matched Monel 400 stud bolt and heavy hex nut sets from the same certified UNS N04400 heat — one MTC, one PMI report, one COC covering the complete assembly. Simplifies inspection and documentation for seawater flange joints. Add Monel 400 washers for a fully matched three-component set.
DIN 934 & ASME B18.2.2 Monel 400 Nut Dimensions
Standard dimensions per DIN 934 (standard hex) and ASME B18.2.2 (heavy hex). All in mm. Inch UNC/UNF and non-standard AF on request to sales@akbarfasteners.in.
| Bolt Size | Thread Pitch | Std AF (s) mm | Std Ht (m) mm | Heavy AF (s) mm | Heavy Ht (m) mm | Standard | Condition |
|---|---|---|---|---|---|---|---|
| METRIC HEX NUTS — DIN 934 & ASME B18.2.2 (UNS N04400 · ASTM B164 · ANNEALED) | |||||||
| M6 | 1.0 mm | 10.0 | 5.0 | — | — | DIN 934 | Annealed |
| M8 | 1.25 mm | 13.0 | 6.5 | — | — | DIN 934 | Annealed |
| M10 | 1.5 mm | 17.0 | 8.0 | — | — | DIN 934 | Annealed |
| M12 | 1.75 mm | 19.0 | 10.0 | 21.0 | 12.0 | DIN 934 / B18.2.2 | Annealed |
| M16 | 2.0 mm | 24.0 | 13.0 | 26.9 | 16.0 | DIN 934 / B18.2.2 | Annealed |
| M20 | 2.5 mm | 30.0 | 16.0 | 33.5 | 20.0 | DIN 934 / B18.2.2 | Annealed |
| M24 | 3.0 mm | 36.0 | 19.0 | 40.4 | 24.0 | DIN 934 / B18.2.2 | Annealed |
| M30 | 3.5 mm | 46.0 | 24.0 | 50.8 | 30.0 | DIN 934 / B18.2.2 | Annealed |
| M36 | 4.0 mm | 55.0 | 29.0 | 60.3 | 36.0 | DIN 934 / B18.2.2 | Annealed |
| M42 | 4.5 mm | 65.0 | 34.0 | 71.0 | 42.0 | DIN 934 / B18.2.2 | Annealed |
| M48 | 5.0 mm | 75.0 | 38.0 | 82.6 | 48.0 | DIN 934 / B18.2.2 | Annealed |
| M56 – M100 | 5.5–6.0 mm | Custom | Custom | Custom | Custom | B18.2.2 | Annealed |
| COUPLING NUTS — DIN 6334 | |||||||
| M6 – M48 | Per DIN 13 | Per DIN 934 AF | 3× Bolt Dia. | — | — | DIN 6334 | Annealed |
| INCH THREAD NUTS — ASME B18.2.2 | |||||||
| ¼” – 4″ UNC/UNF | Per ASME B1.1 | Per B18.2.2 | Per B18.2.2 | Heavy Hex Avail. | Per B18.2.2 | B18.2.2 | Annealed |
* Matched stud bolt + heavy hex nut sets with single MTC/COC available. Contact sales@akbarfasteners.in
Four Reasons to Use Monel 400 Nuts with Monel 400 Bolts
Using a stainless or carbon steel nut against a Monel 400 stud bolt to reduce cost is technically valid in dry atmospheric service — but in any application involving seawater immersion, splash zone exposure, or HF acid contact, dissimilar metal nuts cause failures that the Monel 400 stud bolt was specifically chosen to prevent. The four reasons below explain the failure mechanics and why Akbar Fasteners Pvt. Ltd. always recommends the fully matched Monel 400 assembly.
The same principle applies across our full range — matched Monel 400 washers complete the three-component galvanic-neutral assembly. For higher strength service, the same matched-heat principle applies to our Monel K500 nuts.
Zero Galvanic Corrosion at Thread Interface
Identical alloy throughout the joint means zero electrochemical potential difference. No galvanic cell forms between nut and stud in seawater electrolyte — the most common failure mode for mixed-alloy marine fastener assemblies.
No Crevice Attack in Thread Root
Monel 400 resists crevice corrosion in the stagnant seawater trapped in the thread root between nut and stud — where oxygen depletion creates aggressive local chemistry that rapidly attacks 316L stainless in the same geometry.
No Thread Seizure — No Lock-Up
Matched Monel 400 nut-to-Monel 400 stud thread contact does not gall or seize in seawater service. Dissimilar metals corrode differentially at the interface, producing corrosion products that lock the nut permanently to the stud in permanent seawater immersion.
Single MTC Covers Complete Assembly
Stud bolt, nut, and washer from the same UNS N04400 certified heat carry one mill test certificate and one PMI verification report — simplifying TPI inspection and vendor document submission for offshore and naval projects.
Standards We Manufacture & Test To
Same quality system as our Hastelloy B3 stud bolts and complete exotic alloy range. Full heat traceability from mill certificate to dispatch.
Industry Applications
Wherever Monel 400 bolts and stud bolts are specified — the nut must be Monel 400 too, for galvanic compatibility and sustained joint integrity.
Seawater Systems
desalination plant joints
Marine & Offshore
shipboard pipe joints
HF Alkylation Units
HF service assemblies
Chemical Processing
brine equipment joints
Naval & Defence
shipboard assemblies
Pump & Valve Bodies
marine valve nut sets
Power Generation
condenser nozzle nuts
Marine Hanger Systems
offshore support systems
Complete Documentation Package
Heat & Lot Traceable
Conformance
100% Lots Verified
Tensile · Hardness
TÜV · BV · Lloyds
Matched Monel 400 Assembly Components
Order nuts, stud bolts, and washers from the same certified UNS N04400 heat — one MTC, one PMI, zero galvanic risk throughout the joint.
Monel 400 Stud Bolts
Fully threaded and double-end stud bolts, Class 150–2500, M12–M100 up to 3,000mm. Supply with these matching Monel 400 heavy hex nuts from same certified heat.
View Page →Monel 400 Washers
Flat and spring washers in Monel 400, M5–M100. Complete the three-component galvanic-neutral assembly — bolt, nut, and washer all matched to the same N04400 heat.
View Page →Monel K500 Nuts
Age-hardened version for higher-strength marine assemblies. ≥1000 MPa. For Class 1500/2500 pressure joints and subsea applications where Monel 400 strength is insufficient.
View Page →Hastelloy B3 Stud Bolts
For HCl and reducing acid service where Monel 400 is not specified. Near-zero corrosion in HCl at all concentrations. Matched B3 nuts from same heat.
View Page →Need Monel 400
Nuts Now?
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