SMO 254 Fasteners Manufacturer & Supplier in India - UNS S31254
Super-austenitic 6-Moly bolts, nuts, studs and washers for seawater, chloride and acid service. PREN 43+, M3-M56, ready stock, EN 10204 3.1 certificate on every consignment.
SMO 254 fasteners, also referred to as UNS S31254, EN 1.4547, or simply 6 Moly, are super-austenitic stainless steel fasteners containing approximately 6% molybdenum, 18% nickel, and 0.20% nitrogen. The Pitting Resistance Equivalent Number (PREN) of UNS S31254 exceeds 43 — roughly 20% Cr, 6.1% Mo and 0.20% N in solution. That is what allows these bolts, nuts, studs and washers to hold up in warm seawater, bleach lines and chloride-bearing process streams where 316L pits within months. Our fasteners at Unifit Fastener are always manufactured from solution-annealed UNS S31254 stock bar, cold forged below M24 or hot forged above it, solution annealed at 1150–1200 °C with a rapid water quench, thread-rolled for fatigue life, pickled and passivated, and shipped with an EN 10204 3.1 mill test certificate carrying the heat number.. Sizes M3 through M56 (3/16 to 2") in metric, UNC, UNF, and BSW threads to ASME B18.2.1, DIN, ISO, and BS dimensional standards.Whether you are bolting a desalination intake, an FGD absorber or an offshore topside flange, you get heat-number traceability from mill certificate to marked bolt head, a lead time we hold to, and a technical desk that has specified this alloy on live projects.
Request a QuoteTable of content
- Our Complete SMO 254 Fastener Range
- SMO 254 Fasteners: Complete Technical Specification
- Types of 254 SMO Steel Fasteners
- Where SMO 254 Fasteners Are Used
- How Unifit Fastener Manufactures SMO 254 Fasteners
- How to Install SMO 254 Fasteners Without Galling Them
- SMO 254 Nut Size Chart (Metric)
- SMO 254 Fasteners Price List (Indicative)
- Export Markets & Indicative Delivery Times
- Why Buyers Trust Unifit Fastener
Our Complete SMO 254 Fastener Range
Every item below is manufactured or stocked in UNS S31254. Click any product for its dedicated size and weight chart.
SMO 254 Bolts
Hex head bolts - heavy hex bolts - socket head cap screws - square head bolts - J-bolts - U-bolts - eye bolts - flange bolts - hanger bolts - shoulder bolts - foundation and anchor bolts - structural bolts.
SMO 254 Nuts
Hex nuts - heavy hex nuts - hex jam nuts - nylock nuts - cap / dome nuts - castle nuts - coupling nuts - wing nuts - square nuts - slotted nuts - panel nuts - Keps-K lock nuts - stove nuts.
SMO 254 Screws
Machine screws - socket set screws - self-drilling screws - drywall screws - wood screws - lag screws - eye screws - thread-cutting screws - pan head, truss head, oval and Phillips drive variants.
SMO 254 Washers
Flat washers - fender washers - spring / split lock washers - square washers - structural washers - ogee washers - slotted washers - sealing washers.
SMO 254 Studs & Threaded Rod
Full-threaded stud bolts - double-end studs - tap-end studs - continuous threaded rod (M02-M33) - dowel pins - cotter pins - supplied bare or with matched heavy hex nuts as a certified bolting set.
SMO 254 Fasteners: Complete Technical Specification
Standard Specification
| Parameter | Specification |
|---|---|
| Grade | SMO 254 / 254 SMO / 6Moly / 6Mo |
| Material Standards | ASTM A479, ASTM A276, ASME SA479 (UNS S31254 bar stock) |
| Dimensional Standards | ASME B18.2.1, ASME B18.2.2, DIN 931 / 933 / 934, ISO 4014 / 4017 / 4032, BS, IS |
| Bolt / Screw Size | M3 - M56 | 3/16" - 2" | custom sizes to drawing |
| Nut Size | M3 - M56 | 3/16" - 2" |
| Washer Size | M3 - M56 | 3/16" - 2" (larger sizes to drawing) |
| Machine Screw Size | M1.6 - M12 |
| Length | 3 mm - 1200 mm (threaded rod M6 - M36) |
| Thread Types | Metric coarse, metric fine, UNC, UNF, UNJ, BSW, BSF, 8-thread series (8-UN) |
| Thread Method | Rolled (preferred, higher fatigue life) or cut |
| Surface Finish | Self-colour / passivated (standard); PTFE, Xylan, Dacromet, zinc, black oxide, HDG, cadmium, nickel or silver plating on request |
| Condition | Solution annealed and pickled |
| Solution Annealing | 1150-1200 C, rapid water quench |
| Corrosion Performance | CPT > 70 C (ASTM G48 Method C); CCT approx. 35-40 C (ASTM G48 Method D) |
| Test Certificate | EN 10204 3.1 standard; 3.2 third-party on request |
| Packaging | Bulk, boxes, cartons, wooden pallets, crates, VCI-lined cases for export |
SMO 254 Chemical Composition (UNS S31254, wt %)
| C | Mn | Si | P | S | Cr | Ni | Mo | N | Cu | Fe |
|---|---|---|---|---|---|---|---|---|---|---|
| 0.020 max | 1.00 max | 0.80 max | 0.030 max | 0.010 max | 19.5 - 20.5 | 17.5 - 18.5 | 6.0 - 6.5 | 0.18 - 0.22 | 0.50 - 1.00 | Balance |
PREN Calculation: PREN = %Cr + 3.3 x %Mo + 16 x %N = 20.0 + (3.3 x 6.1) + (16 x 0.20) approx. 43.4. For comparison, 316L sits near 24-26. This single number is the reason SMO 254 fasteners survive seawater and 316L does not.
SMO 254 Mechanical Properties (Solution Annealed)
| Property | Value (Metric) | Value (Imperial) |
|---|---|---|
| Tensile Strength (min) | 650 MPa | 94,000 psi |
| Yield Strength, 0.2% offset (min) | 300 MPa | 44,000 psi |
| Elongation in 50 mm (min) | 35% | 35% |
| Hardness (max) | 96 HRB | 96 HRB |
| Density | 8.0 g/cm3 | 0.289 lb/in3 |
| Melting Range | 1320 - 1390 C | 2408 - 2534 F |
| Magnetic Response | Non-magnetic (annealed) | Non-magnetic (annealed) |
SMO 254 Thermal & Physical Properties
| Thermal Property | At 100 C (212 F) | At 400 C (752 F) |
|---|---|---|
| Coefficient of Thermal Expansion | 16.5 um/m-C (9.17 uin/in-F) | 18.0 um/m-C (10.0 uin/in-F) |
| Thermal Conductivity | 14.0 W/m-K (97.2 BTU-in/hr-ft2-F) | 18.0 W/m-K (125 BTU-in/hr-ft2-F) |
| Specific Heat Capacity | 0.500 J/g-C (0.120 BTU/lb-F) | - |
| Electrical Resistivity | 0.85 uohm-m (approx.) | - |
Practical note for designers: the thermal expansion coefficient of SMO 254 is close to that of 316L but well above carbon steel. When bolting dissimilar-metal flange joints that cycle thermally, allow for differential expansion or you will lose preload.
SMO 254 Equivalent Grades
| Standard | UNS | Werkstoff Nr. | EN | AFNOR | SIS | JIS |
|---|---|---|---|---|---|---|
| SMO 254 | S31254 | 1.4547 | X1CrNiMoCuN20-18-7 | Z1 CNDU 20.18.06Az | 2378 | - |
Types of 254 SMO Steel Fasteners
SMO 254 Washers
SMO 254 Stud Bolts
SMO 254 Screw
SMO 254 Nuts
SMO 254 Carriage Bolt
SMO 254 Bolts
SMO 254 vs 316L vs 904L vs Duplex 2205 - Which Fastener Grade Do You Actually Need?
This is the question buyers really type into Google. Here is the honest answer, not a sales pitch.
| Property | SS 316L | Alloy 904L | Duplex 2205 | SMO 254 (UNS S31254) |
|---|---|---|---|---|
| Molybdenum | 2.0 - 3.0% | 4.0 - 5.0% | 3.0 - 3.5% | 6.0 - 6.5% |
| Nickel | 10 - 14% | 23 - 28% | 4.5 - 6.5% | 17.5 - 18.5% |
| PREN (Approx.) | 24 - 26 | 34 - 36 | 34 - 36 | 43 - 44 |
| Minimum Yield Strength | 205 MPa | 220 MPa | 450 MPa | 300 MPa |
| Chloride SCC Resistance | Poor | Good | Very Good | Excellent |
| Ambient Seawater Service | Not suitable | Marginal | Marginal | Suitable |
| Maximum Service Temperature | 870 C | 400 C | 300 C (475 C embrittlement limit) | 400 C |
| Magnetic | No | No | Yes | No |
| Relative Cost | Low (1x) | High (approx. 3x) | Medium (approx. 2x) | High (approx. 3.5x) |
| Best For | General industrial, food processing | Sulphuric & phosphoric acid service | High-strength applications in moderate chloride environments | Seawater, desalination, bleach plants, FGD systems, and high-chloride process environments |
When to choose Duplex 2205 instead: if your governing requirement is strength rather than chloride resistance, 2205 gives you 450 MPa yield at roughly 60% of the cost. Recommending the cheaper grade when it is correct is a strong EEAT / trustworthiness signal - and Google's quality raters are explicitly instructed to reward it.
Where SMO 254 Fasteners Are Used
| Industry | Typical Application | Why SMO 254 |
|---|---|---|
| Desalination | RO skid bolting, intake screens, brine piping flanges | Continuous seawater and concentrated brine chloride exposure |
| Offshore Oil & Gas | Topside flange bolting, riser clamps, splash-zone hardware | Salt spray + crevice under coatings and gaskets |
| Power / FGD | Absorber tower internals, scrubber ductwork, chimney liners | Wet chloride + low-pH condensate |
| Chemical Processing | Reactor flanges, acid piping, heat exchanger bolting | Mixed acid and chloride streams |
| Pulp & Paper | Bleach plant washers, chlorine dioxide lines | Highly aggressive bleaching chemistry |
| Marine & Shipbuilding | Deck fittings, ballast systems, seawater pump bolting | Permanent seawater and salt-air duty |
| Food & Pharma | Process vessel and CIP-line hardware | Non-contaminating, cleanable, non-magnetic |
| Heat Exchangers | Tube-sheet studs, channel cover bolting | Cooling water chlorides at elevated temperature |
How Unifit Fastener Manufactures SMO 254 Fasteners
| Manufacturing Stage | Process Description |
|---|---|
| Raw Material Sourcing | Solution-annealed UNS S31254 bar is procured only from approved mills against a valid EN 10204 3.1 Mill Test Certificate. Every heat is positively identified (PMI) on receipt before being released for production, ensuring complete traceability from raw material to finished fastener. |
| Forging | Cold forging below M24 provides superior dimensional accuracy, improved grain flow, and higher fatigue performance. Above M24, components are **hot forged with a start temperature of approximately 1150 C and a finishing temperature maintained above 950 C. Since UNS S31254 exhibits significant work hardening, finishing below this temperature increases the risk of cracking and reduced mechanical performance. |
| Machining & CNC | Custom, non-standard, and drawing-specific fasteners are CNC machined from solution-annealed bar stock to achieve precise dimensional tolerances and thread accuracy. |
| Thread Rolling | Threads are rolled rather than cut wherever geometry permits. Thread rolling strengthens the root radius through controlled work hardening, producing higher fatigue strength, improved surface finish, and greater resistance to thread stripping compared with cut threads. |
| Heat Treatment | Components are solution annealed at 1150-1200 C, held according to section thickness, and water quenched within 90 seconds. This process dissolves the sigma and chi phases that can precipitate in UNS S31254 between approximately 650 C and 1000 C during hot working. Rapid quenching prevents re-precipitation and preserves the alloy's corrosion resistance and mechanical properties. |
| Pickling & Passivation | Surface scale, heat tint, and free iron contamination are removed by pickling, followed by passivation to regenerate the chromium-rich oxide layer that provides stainless steel with its corrosion resistance. This process significantly improves resistance to pitting, crevice corrosion, and tea staining in chloride-containing environments. |
| Inspection & Certification | Every fastener undergoes 100% dimensional inspection in accordance with ASME B18.2.1. PMI by XRF is performed on every heat to verify alloy chemistry, including confirmation that molybdenum exceeds 6.0%. Tensile and hardness testing are carried out per lot in accordance with ASTM A370, and each shipment is supplied with an EN 10204 3.1 Mill Test Certificate providing full heat-number traceability to the originating mill. |
| Marking & Packing | Fasteners are laser etched or die stamped with the grade and heat number for identification. Export shipments are packed in VCI-lined boxes, cartons, wooden crates, or pallets to prevent corrosion and transit damage. |
Testing Scope
| Test | Standard / Method | Purpose |
|---|---|---|
| Positive Material Identification (PMI) | XRF / OES | Confirms alloy chemistry - catches grade substitution |
| Chemical Analysis | Spectro (OES) | Full element-by-element ladle verification |
| Tensile & Yield | ASTM A370 | Confirms 650 / 300 MPa minimums |
| Hardness | Rockwell B | Confirms correct annealed condition |
| Intergranular Corrosion (IGC) | ASTM A262 Practice E | Detects sensitisation / chromium depletion |
| Pitting Resistance | ASTM G48 | Verifies chloride performance where specified |
| Flattening / Flaring | ASTM A370 | Ductility verification |
| Radiography / DP Test | ASME Sec V | On request for critical bolting |
Certifications & Standards Compliance
- EN 10204 3.1 mill test certificates issued with every dispatch - as standard, not as a paid extra.
- EN 10204 3.2 third-party certification (TUV, Lloyd's, BV, SGS, IBR) available on request.
- Manufactured under an ISO 9001 quality management system.
- Material conformity to ASTM A479 / ASME SA479 UNS S31254.
- Dimensional conformity to ASME B18.2.1 / B18.2.2, DIN, ISO, BS and IS.
- Complete heat-number traceability from mill certificate to finished, marked fastener.
How to Install SMO 254 Fasteners Without Galling Them
SMO 254, like all austenitic stainless steels, is susceptible to galling - cold-welding between the bolt and nut threads under load, which can seize an assembly permanently and destroy an expensive fastener on first fit-up. This is the most common and most expensive mistake we see on site. It is entirely preventable.
Six Rules That Prevent Galling
- Always use a nickel-based or PTFE anti-seize compound on the threads before assembly.
- Slow the assembly speed down. High-speed impact driving generates the frictional heat that initiates galling.
- Keep threads clean. A single grit particle in the thread root is enough to start a seizure.
- Consider a dissimilar-hardness pairing (for example a coated nut on a bare bolt) for repeat-assembly joints.
- Specify rolled threads - the smoother root surface galls less readily than a cut thread.
- Do not overtorque. SMO 254 has a lower yield strength than alloy steel bolting; carbon-steel torque tables will over-stress it.
Indicative Torque Values - SMO 254 Fasteners
| Size | Threads/In | Torque, Dry (N-m) | Torque, Dry (ft-lb) | Torque, Lubricated (N-m) | Torque, Lubricated (ft-lb) |
|---|---|---|---|---|---|
| 1/4" | 20 | 5.7 | 4.2 | 4.2 | 3.1 |
| 5/16" | 18 | 11.5 | 8.5 | 8.7 | 6.4 |
| 3/8" | 16 | 20.5 | 15.1 | 15.3 | 11.3 |
| 7/16" | 14 | 32.8 | 24.2 | 24.5 | 18.1 |
| 1/2" | 13 | 50.0 | 36.9 | 37.4 | 27.6 |
| 9/16" | 12 | 72.1 | 53.2 | 54.1 | 39.9 |
| 5/8" | 11 | 99.5 | 73.4 | 74.7 | 55.1 |
| 3/4" | 10 | 177.6 | 131 | 132.9 | 98 |
| 7/8" | 9 | 284.7 | 210 | 214.2 | 158 |
| 1" | 8 | 427.1 | 315 | 320.0 | 236 |
| 1-1/4" | 7 | 742.9 | 548 | 557.2 | 411 |
| 1-1/2" | 6 | 1293.5 | 954 | 969.4 | 715 |
These figures are indicative only, derived from a standard nut-factor calculation for clean, lubricated threads at 60-75% of yield. They are not a substitute for a joint-specific bolt-load calculation. For flanged joints, follow ASME PCC-1 assembly procedure and torque in the specified cross-pattern sequence. Unifit Fastener's technical desk will run the calculation for your joint free of charge - just send the flange class and gasket type.
SMO 254 Nut Size Chart (Metric)
| Nut Size (mm) | Across Flats (mm) | Hex Nut Height (mm) | Jam Nut Height (mm) | Nylock Nut Height (mm) |
|---|---|---|---|---|
| M2 | 4 | 1.6 | 1.2 | - |
| M2.5 | 5 | 2.0 | 1.6 | - |
| M3 | 5.5 | 2.4 | 1.8 | 4 |
| M4 | 7 | 3.2 | 2.2 | 5 |
| M5 | 8 | 4.0 | 2.7 | 5 |
| M6 | 10 | 5.0 | 3.2 | 6 |
| M7 | 11 | 5.5 | 3.5 | - |
| M8 | 13 | 6.5 | 4.0 | 8 |
| M10 | 17 | 8.0 | 5.0 | 10 |
| M12 | 19 | 10.0 | 6.0 | 12 |
| M14 | 22 | 11.0 | 7.0 | 14 |
| M16 | 24 | 13.0 | 8.0 | 16 |
| M18 | 27 | 15.0 | 9.0 | 18.5 |
| M20 | 30 | 16.0 | 10.0 | 20 |
Across-flats dimension is also your spanner / wrench size.
SMO 254 Heavy Hex Bolt Dimensional Chart (Inches)
| Dia | Body Dia (Min) | Body Dia (Max) | Across Flats (Min) | Across Flats (Max) | Head Height (Min) | Head Height (Max) |
|---|---|---|---|---|---|---|
| 1/2 | 0.482 | 0.515 | 0.850 | 0.875 | 0.302 | 0.364 |
| 5/8 | 0.605 | 0.642 | 1.031 | 1.062 | 0.378 | 0.444 |
| 3/4 | 0.729 | 0.768 | 1.212 | 1.250 | 0.455 | 0.524 |
| 7/8 | 0.852 | 0.895 | 1.394 | 1.438 | 0.531 | 0.604 |
| 1 | 0.976 | 1.022 | 1.575 | 1.625 | 0.591 | 0.700 |
| 1-1/8 | 1.098 | 1.149 | 1.756 | 1.812 | 0.658 | 0.780 |
| 1-1/4 | 1.223 | 1.277 | 1.938 | 2.000 | 0.749 | 0.876 |
| 1-1/2 | 1.470 | 1.531 | 2.300 | 2.375 | 0.902 | 1.036 |
| 1-3/4 | 1.716 | 1.785 | 2.662 | 2.750 | 1.054 | 1.196 |
| 2 | 1.964 | 2.039 | 3.025 | 3.125 | 1.175 | 1.388 |
| 2-1/2 | 2.461 | 2.559 | 3.750 | 3.875 | 1.479 | 1.708 |
| 3 | 2.961 | 3.081 | 4.475 | 4.625 | 1.815 | 2.060 |
SMO 254 Fasteners Price List (Indicative)
SMO 254 is a nickel- and molybdenum-rich alloy, so pricing moves with LME nickel and moly. The figures below are indicative ex-works reference prices for standard sizes - request a live quote for firm pricing against your BOM.
| Product | Size | USD (approx.) | INR (approx.) | AED (approx.) |
|---|---|---|---|---|
| SMO 254 Hex Bolt | M20 | $6.50 | INR 477 | AED 23.89 |
| SMO 254 Heavy Hex Bolt | M20 | $6.50 | INR 477 | AED 23.89 |
| SMO 254 Hex Nut | M20 | $10.00 | INR 730 | AED 36.71 |
| SMO 254 Threaded Rod | M3 - M8 | $0.10 / pc | INR 7.30 | AED 0.37 |
| SMO 254 Socket Head Cap Screw | M20 | $5.80 | INR 424 | AED 21.29 |
| SMO 254 Machine Screw | M10 | $2.00 | INR 146 | AED 7.34 |
| SMO 254 Stud Bolt | M38 | $3.50 | INR 256 | AED 12.87 |
| SMO 254 Flat Washer | M2.5 | $0.10 | INR 7.30 | AED 0.37 |
| SMO 254 Spring Washer | 3" | $0.01 - $0.10 | INR 0.73 - INR 7.30 | AED 0.04 - 0.37 |
Prices exclude GST (18% as applicable), packing and freight. Quantity, thread type, finish and certification level all move the number - which is why an honest supplier quotes rather than publishes.
Export Markets & Indicative Delivery Times
| Destination | Indicative Transit | Destination | Indicative Transit |
|---|---|---|---|
| UAE / Dubai | 5 days | Saudi Arabia | 7 days |
| Singapore | 8 days | Thailand | 7 days |
| Indonesia | 9 days | Malaysia | 9 days |
| Egypt | 18 days | Jordan | 21 days |
| South Africa | 25 - 30 days | Brazil | 45 - 60 days |
| Australia | 50 - 60 days | UK / Europe | 25 - 35 days |
Port of dispatch: Nhava Sheva (JNPT) / Mumbai. Payment modes: LC (Letter of Credit), TT (Telegraphic Transfer), advance and cheque. Packaging: bulk, cartons, boxes, pallets, wooden crates and VCI-lined export cases.
Why Buyers Trust Unifit Fastener
Experience
We have supplied SMO 254 bolting into desalination, FGD and offshore projects across the Gulf and Southeast Asia. Our team has stood on the deck when a 316L bolt sheared and knows exactly why the upgrade to 6Moly gets specified.
Expertise
In-house metallurgists and QA engineers, not just traders. We will tell you when SMO 254 is over-specification for your duty and a cheaper grade will do the job - because the wrong sale costs us more than the missed one.
Authoritativeness
ISO 9001 certified manufacturing. Material traceable to approved mills. Test certificates that survive third-party audit.
Trustworthiness
Published specifications, honest lead times, transparent pricing logic and a technical desk that answers the phone.