Unifit Fastener is a specialist manufacturer, exporter and ready-stock supplier of Stainless Steel 317 and 317L fasteners, which have been designed to withstand the most severe conditions in industrial settings that would cause regular steel to corrode. Grade 317 is an austenitic chromium-nickel-molybdenum stainless steel with a higher molybdenum content (3–4%) which provides significantly better resistance to pitting and crevice corrosion than 304 or 316. The 317L variant reduces the carbon limit to avoid carbide precipitation during welding, and is recommended where the fabrication process and corrosion resistance are both important considerations. Whether on petrochemical refineries, pulp and paper mills, offshore platforms or flue gas desulphurisation systems, our 317/317L bolts, nuts, studs, screws and washers deliver the performance required when exposed to chlorides, dilute sulphuric and phosphoric acids, and long-term high temperatures. All fasteners are manufactured to meet ASTM F593/F594 standards and ASME standards and are accompanied by mill test certificates, PMI verification and third-party inspection upon request. Technical precision, competitive pricing and rapid worldwide dispatch – so your project doesn't wait on hardware – Unifit Fastener has a deep ready stock of sizes from M3 to M56 (3/16" to 2") and up to 200 mm long.
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- What Are SS 317 / 317L Fasteners?
- Stainless Steel 317/317L Fasteners Available Types
- Stainless Steel 317 / 317L Fasteners Specifications
- SS 317 / 317L Fasteners Chemical Composition (%)
- Mechanical & Physical Properties
- 317 vs 317L vs 316: Which Grade Do You Need?
- Stainless Steel 317 / 317L Fastener Dimensions
- SS 317 / 317L Fasteners Applications & Industries
- Manufacturing Process & Quality Assurance
- Standards & Certifications
- Global Supply & Dispatch
- FAQs - SS 317 / 317L Fasteners
What Are SS 317 / 317L Fasteners?
Stainless Steel 317 fasteners belong to the austenitic 300-series family. The grade's defining feature is its higher molybdenum and nickel loading, which stabilises the austenitic structure and dramatically improves resistance to localised corrosion in chloride- and acid-bearing media. This makes 317 a natural step up from 316 when service conditions turn aggressive.
317L is the low-carbon derivative (carbon held to 0.035% max versus 0.08% for 317). Reducing carbon suppresses the formation of chromium carbides at grain boundaries during welding — the mechanism behind intergranular corrosion — so 317L fasteners can be welded into heavy sections and still retain full corrosion resistance without a post-weld solution. Both grades offer excellent creep-rupture and tensile strength at elevated temperature, good formability and a clean, corrosion-resistant surface finish.
Why engineers specify 317 / 317L
- Superior pitting & crevice corrosion resistance in chloride environments.
- Excellent performance against dilute sulphuric, phosphoric and organic acids.
- Retains strength and oxidation resistance at high service temperatures.
- 317L's low carbon prevents weld-zone sensitisation — ideal for fabricated assemblies.
- Non-magnetic, hygienic and easy to maintain across long service life.
Stainless Steel 317/317L Fasteners Available Types
Stainless Steel 317_317L Washers
Stainless Steel 317_317L Stud Bolts
Stainless Steel 317_317L Screws
Stainless Steel 317_317L Nuts
Stainless Steel 317_317L Bolts
Stainless Steel 317_317L Anchor Bolts
Stainless Steel 317 / 317L Fasteners Specifications
| Attribute | Specification |
|---|---|
| Standards | ASTM F593, F594 / ASME SF593, SF594 / ASTM A193, A194 (bolting, as applicable) |
| Grades | SS 317, SS 317L (UNS S31700 / S31703) |
| Bolt / Screw Size | M3 – M56 | 3/16" to 2" |
| Nut Size | M3 – M56 | 3/16" to 2" |
| Washer Size | M3 – M56 | 3/16" to 2" |
| Machine Screw Size | M1.6 – M12 |
| Self-Tapping Screw | No. 2 – No. 14 |
| Length | 3 mm to 200 mm |
| Threads | UNF, UNC, BSW, BSF, Metric — or as required |
| Form Standards | DIN 931, 933, 934, 970, 976, 7991, 125; ISO 4014/4017/4032/4033; ANSI B18.2.1 / B18.3 |
| Surface Coating | PTFE, Xylan, zinc plating, hot-dip galvanising, phosphate, cadmium, Teflon |
SS 317 / 317L Fasteners Equivalent Grade Cross-Reference
| Grade | Werkstoff Nr. | UNS | JIS | EN |
|---|---|---|---|---|
| SS 317 | 1.4449 | S31700 | SUS 317 | — |
| SS 317L | 1.4438 | S31703 | SUS 317L | X2CrNiMo18-15-4 |
SS 317 / 317L Fasteners Chemical Composition (%)
Per ASTM specification. Iron (Fe) constitutes the balance.
| Grade | C | Mn | Si | P | S | Cr | Mo | Ni | N |
|---|---|---|---|---|---|---|---|---|---|
| SS 317 | 0.08 | 2.0 | 1.0 | 0.045 | 0.030 | 18.0–20.0 | 3.0–4.0 | 11.0–14.0 | — |
| SS 317L | 0.035 | 2.0 | 0.75 | 0.045 | 0.030 | 18.0–20.0 | 3.0–4.0 | 11.0–15.0 | 0.10 |
Note: values shown are maximums unless a range is given. The higher Mo and Ni levels versus 316 are precisely what deliver 317's enhanced corrosion performance.
Mechanical & Physical Properties
SS 317 / 317L Fasteners Mechanical Properties (317L, minimum values)
| Property | Value (Metric) | Value (Imperial) |
|---|---|---|
| Tensile Strength | 515 MPa min | 75,000 psi |
| Yield Strength (0.2% offset) | 205 MPa min | 30,000 psi |
| Elongation (in 50 mm) | 35% min | 35% min |
| Hardness (Rockwell B) | 95 HRB max | 95 HRB max |
| Hardness (Brinell) | 217 HB max | 217 HB max |
| Standard | Product | Typical Property Classification |
|---|---|---|
| ASTM F593 | Bolts, Hex Bolts, Cap Screws, Stud Bolts, Threaded Rods | Property classes as specified by ASTM F593, depending on alloy designation and cold-work condition |
| ASTM F594 | Hex Nuts, Heavy Hex Nuts, Lock Nuts | Matching property classes for use with ASTM F593 fasteners |
Physical Properties
| Property | SS 317 | SS 317L |
|---|---|---|
| Density | 8.0 g/cm³ | 7.9 g/cm³ |
| Melting Point | 1454 °C (2650 °F) | 1400 °C (2550 °F) |
| Modulus of Elasticity | ≈ 200 GPa (29 × 10⁶ psi) | ≈ 200 GPa (29 × 10⁶ psi) |
| Thermal Conductivity | ≈ 14.6 W/m·K | ≈ 14.6 W/m·K |
| Electrical Resistivity | ≈ 74 µΩ·cm | ≈ 74 µΩ·cm |
317 vs 317L vs 316: Which Grade Do You Need?
| Property | SS 316 | SS 317 | SS 317L |
|---|---|---|---|
| Carbon (max) | 0.08% | 0.08% | 0.035% |
| Molybdenum | 2.0–3.0% | 3.0–4.0% | 3.0–4.0% |
| Pitting Resistance | Good | Better | Better |
| Weldability | Good | Good | Excellent |
| Weld-zone corrosion | Risk if unstabilised | Some risk | Best — no sensitisation |
| Best for | General marine/chemical | Aggressive chlorides | Welded aggressive service |
In short: choose 316 for general corrosion service, 317 when chlorides and acids intensify, and 317L when those same conditions meet welding and fabrication.
Stainless Steel 317 / 317L Fastener Dimensions
All 317/317L fasteners are produced to standard DIN, ISO and ASME dimensions; custom sizes are made to draw. Representative hex-bolt data (mm):
| Nominal (D) | Body Dia (max) | Head Height (max) | Across Flats (max) | Across Corners (max) |
|---|---|---|---|---|
| M10 | 10.00 | 6.63 | 17.00 | 18.48 |
| M12 | 12.00 | 7.76 | 19.00 | 20.78 |
| M16 | 16.00 | 10.32 | 24.00 | 27.71 |
| M20 | 20.00 | 12.88 | 30.00 | 34.64 |
| M24 | 24.00 | 15.44 | 36.00 | 41.57 |
| M30 | 30.00 | 19.48 | 46.00 | 53.12 |
| M36 | 36.00 | 23.38 | 55.00 | 63.51 |
SS 317 / 317L Fasteners Applications & Industries
The corrosion resistance and high-temperature strength of 317/317L make these fasteners the default choice across process and heavy industries:
| Industry | Typical Use |
|---|---|
| Petrochemical & Refineries | Catalytic recovery systems, flares, recuperators, tube hangers |
| Pulp & Paper | Digesters, bleaching lines, chemical recovery equipment |
| Chemical Processing | Reactors, heat exchangers, acid-handling equipment |
| Power Generation | FGD/scrubber systems, cool gasifier internals, pulverised-coal burners |
| Offshore Oil & Gas | Platform structures, subsea and topside assemblies |
| Marine & Seawater | Desalination, seawater cooling, coastal structures |
| Pharmaceutical & Food | Hygienic process equipment and welded structures |
| Steel & Cement Plants | Furnace parts, sintering plant hardware, ore-processing equipment |
Manufacturing Process & Quality Assurance
Unifit Fastener controls quality at every stage, from raw-material verification to final dispatch. Our production combines modern cold and hot forming with precision CNC machining for non-standard geometries.
Production Methods
- Cold forging for high-volume standard fasteners with superior grain flow.
- Hot forging for large-diameter bolts and heavy sections.
- CNC machining for custom heads, special threads and bespoke lengths.
Testing & Inspection
- Chemical analysis by spectro (PMI) — positive material identification.
- Mechanical testing: tensile, yield, elongation and hardness.
- Pitting resistance and intergranular corrosion (IGC) testing.
- Micro & macro examination, flaring and flattening tests.
- Documentation: Mill Test Certificates per EN 10204 3.1, on request.
Standards & Certifications
| Category | Applicable Standards |
|---|---|
| Bolt / Screw | ASTM F593, ASME SF593, A193; DIN 931/933; ISO 4014/4017 |
| Nut | ASTM F594, ASME SF594, A194; DIN 934; ISO 4032/4033 |
| Washer | DIN 125, DIN 9021; ASME B18.22.1 |
| Socket / Cap Screw | ASME B18.3; DIN 912; ISO 4762 |
| Quality System | ISO 9001 quality management; EN 10204 3.1 MTC |
HS Codes
| Grade | HS Code |
|---|---|
| Stainless Steel 904L Bolts & Screws | 7318.15 |
| Stainless Steel 904L Nuts | 7318.16 |
| Stainless Steel 904L Washers | 7318.22 |
| Stainless Steel 904L Threaded Rods / Stud Bolts* | 7318.15 |
Global Supply & Dispatch
Unifit Fastener exports 317/317L fasteners worldwide with secure export packaging and reliable lead times. Ready-stock items ship fastest; custom orders are scheduled to your project timeline.
Key export regions: Middle East (UAE, Saudi Arabia, Qatar, Oman), Europe (Germany, UK, Italy, Netherlands), Asia (Singapore, Malaysia, Japan, South Korea), Africa (Nigeria, South Africa, Egypt), North & South America.
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FAQs - SS 317 / 317L Fasteners
What is the difference between 317 and 317L stainless steel fasteners?
The core difference is carbon content. Standard 317 allows up to 0.08% carbon, while 317L is capped at 0.035%. The lower carbon in 317L prevents chromium-carbide precipitation during welding, so it resists intergranular corrosion in welded joints. Both grades share the same high molybdenum (3–4%) and therefore similar corrosion resistance and strength.
Are 317L fasteners better than 316 for corrosion resistance?
Yes. Grade 317/317L carries more molybdenum (3–4% versus 2–3% in 316) and higher nickel, which improves resistance to pitting and crevice corrosion in chloride- and acid-rich environments. Where 316 begins to pit, 317L typically holds up longer.
Which standards do Unifit 317/317L fasteners meet?
Bolts and screws are produced to ASTM F593 / ASME SF593 and A193; nuts to ASTM F594 / SF594 and A194; with DIN and ISO dimensional standards. Mill Test Certificates to EN 10204 3.1 are available on request.
What sizes and lengths are available?
We supply M3 to M56 and 3/16" to 2" across bolts, nuts and washers, machine screws from M1.6 to M12, and lengths from 3 mm up to 200 mm. Custom sizes are manufactured to order.
Can 317L fasteners be welded without losing corrosion resistance?
Yes — that is the main reason 317L exists. Its low carbon suppresses carbide precipitation in the weld heat-affected zone, so the joint retains corrosion resistance without a post-weld solution anneal.
Ready to source certified SS 317 / 317L fasteners?
Get ASTM F593/F594 compliant fasteners with mill test certificates, PMI verification and worldwide dispatch from Unifit Fastener.
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