Monel 400
Hex Bolts
UNS N04400
Monel 400 Hex Bolts — The Right Choice for Seawater
Monel 400 (UNS N04400) is the annealed nickel-copper alloy with 63–70% Ni and copper as balance — the standard material for bolted connections in seawater, tidal zones, splash zones, HF acid, and marine atmospheric environments where stainless steel fails and engineering strength requirements can be met within the alloy’s ≥480 MPa tensile range.
For hex bolt applications in seawater-cooled heat exchanger covers, marine pump casing flanges, desalination plant equipment, and offshore platform structural connections — Monel 400 hex bolts provide permanent seawater immunity with no crevice corrosion risk, no chloride stress corrosion cracking, and no pitting at any seawater velocity or temperature. A 316L bolt in the same service will pit and seize within months; a Monel 400 bolt in the same service shows no measurable corrosion after years.
When bolt loads exceed the ≥480 MPa range of Monel 400 — for Class 1500/2500 flanges, subsea wellheads, or structural connections requiring Grade 8.8 equivalent strength — step up to our Monel K500 hex bolts at ≥1000 MPa. For strongly reducing acid environments where Monel 400 is not specified, see our Hastelloy 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 | — |
Full Thread Hex Bolts — DIN 933
Thread runs the complete length from head to tip — DIN 933 / ISO 4017. The most common Monel 400 bolt for marine and seawater applications. Used wherever through-holes are used and full thread engagement is required along the bolt length. Standard for seawater pump casing covers, marine heat exchanger channel heads, and desalination plant equipment covers in Class 150–300 service.
Compared to Monel 400 stud bolts, full thread hex bolts are preferred when the joint is assembled and disassembled from one side, and where a hex head is required for wrench access.
| Spec | Details |
|---|---|
| Material | UNS N04400 / Monel 400 |
| Standard | ASTM B164 · DIN 933 · ISO 4017 |
| Size Range | M6 — M100 |
| Thread | Metric coarse DIN 13 |
| Head Form | Hex per DIN 933 AF |
| UTS | ≥ 480 MPa |
| 0.2% YS | ≥ 170 MPa |
| Elongation | ≥ 35% |
| Condition | Annealed |
Partial Thread Hex Bolts — DIN 931
DIN 931 / ISO 4014 — threaded end with a plain (unthreaded) shank between head and thread start. The unthreaded shank carries shear load across the joint interface and prevents thread engagement into the bearing material of connected members — required in many structural design codes. Standard for marine platform structural connections, offshore crane pedestal bolting, and equipment skid base bolting in seawater splash zones. M6–M100.
| Spec | Details |
|---|---|
| Material | UNS N04400 / Monel 400 |
| Standard | ASTM B164 · DIN 931 · ISO 4014 |
| Size Range | M6 — M100 |
| Shank | Plain (unthreaded) per DIN 931 |
| Thread Length | Per DIN 931 grip length |
| UTS | ≥ 480 MPa |
| 0.2% YS | ≥ 170 MPa |
| Condition | Annealed |
Heavy Hex Bolts — ASME B18.2.3.6M
ASME B18.2.3.6M heavy hex bolts have wider across-flats and greater head height than DIN 933 — providing increased wrench bearing area for high-torque tightening and greater head strength. Specified alongside Monel 400 heavy hex nuts for marine pump casings, large seawater flange covers, and desalination plant heat exchanger bonnets requiring maximum torque capacity with Monel 400 corrosion resistance. M12–M100.
| Spec | Details |
|---|---|
| Material | UNS N04400 / Monel 400 |
| Standard | ASTM B164 · ASME B18.2.3.6M |
| Size Range | M12 — M100 |
| Head | Heavy Hex — wider AF, greater height |
| UTS | ≥ 480 MPa |
| Matched Nuts | Monel 400 Heavy Hex Nuts |
| Condition | Annealed |
Flanged Hex Bolts — DIN 6921
Hex bolts with an integral flange (washer face) under the head — eliminates the need for a separate Monel 400 washer, distributes bearing load over a larger area, and prevents bolt head pull-through on soft substrates. Standard per DIN 6921 / ISO 4162. Monel 400 flanged bolts are used in marine GRP hull fittings, composite structural connections, and equipment bases on soft substrates in tidal and splash zones. M6–M64.
| Spec | Details |
|---|---|
| Material | UNS N04400 / Monel 400 |
| Standard | ASTM B164 · DIN 6921 · ISO 4162 |
| Size Range | M6 — M64 |
| Head | Hex with integral serrated flange |
| UTS | ≥ 480 MPa |
| Condition | Annealed |
Inch Thread Hex Bolts — UNC / UNF
Monel 400 hex bolts in UNC (coarse) and UNF (fine) thread per ASME B1.1. Head dimensions per ASME B18.2.1. ¼”–4″ diameter. For US offshore, naval, and export projects specified in imperial dimensions. Same ASTM B164 certified UNS N04400 annealed material — identical seawater and HF acid immunity. Supply with matched inch-thread Monel 400 nuts from same heat on request.
| Spec | Details |
|---|---|
| Material | UNS N04400 / Monel 400 |
| Standard | ASTM B164 · ASME B18.2.1 |
| Size Range | ¼” — 4″ |
| Thread | UNC · UNF per ASME B1.1 |
| Head | Hex per ASME B18.2.1 AF |
| UTS | ≥ 480 MPa |
| Condition | Annealed |
DIN 931 / DIN 933 Monel 400 Hex Bolt Dimensions
Standard dimensions per DIN 931/933 and ISO 4014/4017. All in mm. Partial thread shank length (b) per DIN 931 grip length formula. Non-standard lengths and fine pitch on request to sales@akbarfasteners.in.
| Size (M) | Thread Pitch | AF (s) mm | Head Ht (k) mm | Full Thread (DIN 933) | Part Thread b (DIN 931) | Heavy Hex AF mm | Condition |
|---|---|---|---|---|---|---|---|
| METRIC HEX BOLTS — UNS N04400 · ASTM B164 · ANNEALED | |||||||
| M6 | 1.0 mm | 10.0 | 4.0 | 10–100 mm | 18 mm | — | Annealed |
| M8 | 1.25 mm | 13.0 | 5.3 | 12–200 mm | 22 mm | — | Annealed |
| M10 | 1.5 mm | 17.0 | 6.4 | 16–200 mm | 26 mm | — | Annealed |
| M12 | 1.75 mm | 19.0 | 7.5 | 20–300 mm | 30 mm | 21.0 | Annealed |
| M16 | 2.0 mm | 24.0 | 10.0 | 30–300 mm | 38 mm | 26.9 | Annealed |
| M20 | 2.5 mm | 30.0 | 12.5 | 40–300 mm | 46 mm | 33.5 | Annealed |
| M24 | 3.0 mm | 36.0 | 15.0 | 50–300 mm | 54 mm | 40.4 | Annealed |
| M30 | 3.5 mm | 46.0 | 18.7 | 60–300 mm | 66 mm | 50.8 | Annealed |
| M36 | 4.0 mm | 55.0 | 22.5 | 70–300 mm | 78 mm | 60.3 | Annealed |
| M42 | 4.5 mm | 65.0 | 26.0 | 80–300 mm | 90 mm | 71.0 | Annealed |
| M48 | 5.0 mm | 75.0 | 30.0 | On order | On order | 82.6 | Annealed |
| M56 – M100 | 5.5–6.0 mm | Custom | Custom | On order | On order | Custom | Annealed |
* Fine pitch metric (DIN 13 fine), UNC/UNF inch thread, and non-standard lengths on request. sales@akbarfasteners.in
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
Seawater immunity, HF acid resistance, and marine atmospheric corrosion resistance — for bolted connections where 316L fails and K500 strength is not required.
Seawater Pump Flanges
suction / discharge flanges
Marine & Offshore
equipment skid bases
Desalination Plants
vessel cover bolts
HF Alkylation Units
reactor cover bolts
Oil & Gas
cooling water nozzles
Naval & Shipbuilding
shipboard pipe bolts
GRP / Composite Marine
composite hull fittings
Power Generation
condenser body bolts
Complete Documentation Package
Heat & Lot Traceable
Conformance
100% Lots Verified
Tensile · Hardness
TÜV · BV · Lloyds
Matched Monel 400 Assembly Components
Order bolts, nuts, and washers from the same certified UNS N04400 heat — one MTC, one PMI report, zero galvanic risk throughout the joint.
Monel 400 Nuts
Standard hex, heavy hex, and coupling nuts in annealed Monel 400. Same certified heat as these bolts — zero galvanic couple in seawater service.
View Page →Monel 400 Washers
Plain flat and spring washers in Monel 400, M5–M100. Matched material throughout the assembly — eliminates all galvanic corrosion paths at the joint.
View Page →Monel K500 Hex Bolts
Age-hardened version — ≥1000 MPa UTS. Same Ni-Cu seawater immunity with 3× the strength. For structural and high-load marine bolting applications.
View Page →Monel 400 Fasteners
Full Monel 400 range — stud bolts, threaded rods, socket screws. Complete seawater and HF acid service assembly from one ISO 9001:2015 certified source.
View All →Need Monel 400
Hex Bolts Now?
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