Home » Partially Threaded Hexagon Bolts (DIN 931) — High Tensile Stainless Steel A4-80 (SUS316)

Partially Threaded Hexagon Bolts (DIN 931) — High Tensile Stainless Steel A4-80 (SUS316)

Partially Threaded Hexagon Bolts (DIN 931) — High Tensile Stainless Steel A4-80 (SUS316)

FULLERKREG DIN 931 A4-80 partially threaded hexagon bolts represent the highest standard strength grade available in A4 marine stainless steel (SUS316). Manufactured to Grade A4-80 with a whitened and passivated surface finish, these bolts combine the superior chloride and pitting corrosion resistance of SUS316 (2–3% molybdenum) with a minimum tensile strength of 800 MPa — providing 14% greater strength than A4-70 and making them the preferred choice for high-load structural connections in marine, offshore, chemical, and food-grade environments.

The partially threaded shank — with a smooth unthreaded grip length beneath the head — provides precise shear load transfer through the bolt body, making DIN 931 the preferred choice for structural connections, flanged joints, and machinery where the bolt passes through clearance holes and the thread engages only in the nut or tapped hole. DIN 931 is equivalent to ISO 4014.

Product Specifications

Standard DIN 931 ≡ ISO 4014 (Partially Threaded Hexagon Head Bolts)
Thread Metric coarse per ISO 261 / DIN 13
Thread Coverage Partial thread — unthreaded grip length beneath head
Head Type Hexagon head — driven by open-end wrench, ring spanner, or socket
Material A4 Marine Stainless Steel / SUS316 / 1.4401
Grade A4-80 (highest standard strength grade for A4 stainless)
Surface Finish Whitened & Passivated
Size Range M6 – M36 (A4-80 grade; larger sizes on request)
Length Range 25 mm – 300 mm (size-dependent)
Key Advantage 800 MPa tensile strength + SUS316 corrosion resistance — maximum performance in aggressive environments
Related Standard DIN 933 A4-80 (fully threaded)  |  ISO 4014  |  ISO 3506-1 (stainless fastener properties)

Product Gallery

[Product Photo 1] [Product Photo 2] [Product Photo 3] [Product Photo 4]

Head Dimensions — DIN 931 / ISO 4014

All dimensions in millimeters (mm). Dimensions are identical to A4-70 — the grade designation refers to mechanical properties only, not geometry.

Thread (d) Pitch (mm) s — A/F (mm) e — A/C (mm) k — Head Height (mm) ds — Shank Ø (mm)
M6 1.0 10 11.05 4.0 5.7
M8 1.25 13 14.38 5.3 7.64
M10 1.5 17 18.90 6.4 9.64
M12 1.75 19 21.10 7.5 11.57
M14 2.0 22 24.49 8.8 13.57
M16 2.0 24 26.75 10.0 15.57
M20 2.5 30 33.53 12.5 19.48
M24 3.0 36 39.98 15.0 23.48
M27 3.0 41 45.20 17.0 26.48
M30 3.5 46 50.85 18.7 29.48
M36 4.0 55 60.79 22.5 35.38

* s = across flats (A/F); e = across corners (A/C); k = head height; ds = unthreaded shank diameter (max). All dimensions per DIN 931 / ISO 4014. A4-80 grade available M6–M36 as standard; contact FULLERKREG for larger sizes.

Thread Length (b) — DIN 931 Partial Thread Reference

Thread (d) b — L ≤ 125 mm b — 125 < L ≤ 200 mm b — L > 200 mm
M6 18 24 —
M8 22 28 —
M10 26 32 45
M12 30 36 49
M14 34 40 53
M16 38 44 57
M20 46 52 65
M24 54 60 73
M27 60 66 79
M30 66 72 85
M36 78 84 97

* b = threaded length. Grip length = L − b − k (approximate). Per DIN 931 / ISO 4014.

Material & Grade Properties

Property Value
Material Designation A4 / SUS316 / 1.4401 / 0Cr17Ni12Mo2
Property Class A4-80
Tensile Strength (Rm) ≥ 800 MPa
0.2% Proof Stress (Rp0.2) ≥ 600 MPa
Stress Under Proof Load ≥ 640 MPa (for d ≤ M39)
Hardness ≤ 250 HV
Molybdenum Content 2.0 – 3.0%
Pitting Resistance (PREN) ~24–26
Corrosion Resistance Excellent — superior chloride, pitting & crevice corrosion resistance
Magnetic Slightly magnetic after cold working (strain-hardened to achieve A4-80)
Surface Finish Whitened & Passivated
Temperature Range −50°C to +300°C (continuous service)
Manufacturing Process Strain-hardened (cold worked) to achieve 800 MPa — not heat treated

A4-80 vs A4-70 vs A2-70 — Grade Comparison

Property A4-80 (This Product) A4-70 A2-70
Material SUS316 (Mo 2–3%) SUS316 (Mo 2–3%) SUS304 (no Mo)
Tensile Strength (Rm) ≥ 800 MPa ≥ 700 MPa ≥ 700 MPa
Proof Stress (Rp0.2) ≥ 600 MPa ≥ 450 MPa ≥ 450 MPa
Proof Load Stress ≥ 640 MPa ≥ 580 MPa ≥ 580 MPa
Strength advantage +14% vs A4-70 / A2-70 Baseline Baseline
Chloride resistance Excellent (Mo) Excellent (Mo) Good (no Mo)
Marine / offshore ✅ Best choice — high strength + corrosion resistance ✅ Good ⚠️ Marginal in seawater
Availability (large sizes) M6–M36 standard M6–M64 M6–M64
Cost Highest Medium-high Medium
Best for High-load marine, offshore, chemical structural joints Standard marine & corrosive structural joints General outdoor & mild corrosive environments

Weight Reference Table (kg / 100 pcs)

Approximate weights per 100 pieces. Based on A4 stainless steel density (7.98 g/cm³).

L (mm) M6 M8 M10 M12 M16 M20 M24 M30 M36
25 0.14 0.29 — — — — — — —
30 0.16 0.35 0.62 — — — — — —
40 0.22 0.47 0.85 1.28 2.52 — — — —
50 0.27 0.59 1.07 1.62 3.20 5.64 — — —
60 0.32 0.72 1.29 1.96 3.88 6.85 11.3 — —
70 0.37 0.84 1.51 2.30 4.57 8.06 13.3 — —
80 0.43 0.96 1.73 2.65 5.26 9.27 15.3 28.2 —
100 0.53 1.20 2.17 3.33 6.63 11.7 19.3 35.8 60.5
120 0.64 1.44 2.62 4.02 8.00 14.1 23.4 43.5 73.3
140 0.75 1.68 3.06 4.70 9.37 16.5 27.4 51.2 86.2
160 — 1.92 3.51 5.39 10.74 18.9 31.4 58.8 99.1
180 — 2.16 3.95 6.07 12.11 21.3 35.4 66.5 112
200 — 2.40 4.39 6.76 13.48 23.8 39.5 74.1 125
240 — — 5.28 8.13 16.22 28.6 47.5 89.4 151
300 — — — 10.18 20.33 35.9 59.6 113 190

* Weights are approximate (kg/100 pcs) based on A4 stainless steel density (7.98 g/cm³). Contact FULLERKREG for precise weight certificates and material test reports.

How A4-80 Achieves Higher Strength

  • Strain hardening (cold working): A4-80 achieves its 800 MPa tensile strength through controlled cold working (strain hardening) of the austenitic stainless steel — not through heat treatment or alloying changes.
  • Same material as A4-70: The base material is identical SUS316 — the difference is the manufacturing process. A4-80 undergoes additional cold working to increase dislocation density and raise yield and tensile strength.
  • Slight magnetism: Cold working induces a small amount of martensite in the austenitic matrix, making A4-80 slightly more magnetic than annealed A4-70. This is normal and does not affect corrosion resistance.
  • Size limitation: The cold working process is more practical for smaller diameters. A4-80 is typically available in M6–M36 as standard; larger sizes may require special order.

Typical Applications

  • 🚢 Marine & offshore high-load structures — structural bolting on vessels, offshore platforms, and marine equipment where both high strength and corrosion resistance are required
  • 🌊 Coastal & saltwater high-stress connections — structural joints in tidal zones, jetties, and coastal infrastructure under significant load
  • 🧪 Chemical processing — high-pressure flanges — flange bolting in high-pressure chemical plant in chloride or acid environments
  • 🔧 Pressure vessel & heat exchanger flanges — where both high bolt load and corrosion resistance are specified
  • 🏭 Industrial plant — high-load corrosive environments — where A4-70 strength is insufficient and carbon steel high-tensile bolts would corrode
  • 🛠️ Structural engineering — stainless specified — bridges, walkways, and civil structures where stainless is specified and maximum bolt strength is required

Frequently Asked Questions

Q: What is the difference between A4-80 and A4-70?
A: Both are A4 (SUS316) marine stainless steel with identical corrosion resistance. A4-80 achieves a higher tensile strength (≥800 MPa vs ≥700 MPa) and proof stress (≥600 MPa vs ≥450 MPa) through additional cold working (strain hardening) during manufacture. Choose A4-80 when the joint design requires higher bolt preload or when replacing carbon steel high-tensile bolts with stainless in a corrosive environment.

Q: Can A4-80 replace carbon steel Grade 8.8 bolts in corrosive environments?
A: A4-80 (800 MPa) is mechanically equivalent to carbon steel Grade 8.8 (800 MPa minimum tensile strength). It can be used as a direct strength-equivalent replacement for Grade 8.8 in corrosive environments where carbon steel would corrode. Always verify with a structural engineer for safety-critical applications.

Q: Why is A4-80 slightly magnetic?
A: The cold working process used to achieve 800 MPa strength induces a small amount of strain-induced martensite in the austenitic stainless matrix, making A4-80 slightly more magnetic than annealed A4-70. This is a normal characteristic of cold-worked austenitic stainless steel and does not affect corrosion resistance or mechanical performance.

Q: What is the difference between DIN 931 and DIN 933 in A4-80?
A: DIN 931 A4-80 is partially threaded — smooth shank beneath the head for shear load transfer. DIN 933 A4-80 is fully threaded. Choose DIN 931 for structural shear-critical connections; choose DIN 933 when maximum thread engagement or grip-length flexibility is needed.

Q: Can stainless steel A4-80 bolts gall during installation?
A: Yes. Cold-worked stainless steel (A4-80) can be more susceptible to galling than annealed grades due to higher surface hardness. Always apply a nickel-based anti-seize compound to threads before installation, especially for M20 and above. Use calibrated torque tools to avoid over-torquing.

Q: What nut should I use with A4-80 bolts?
A: Use A4 stainless steel hexagon nuts (DIN 934 / ISO 4032) — standard A4 nuts are compatible with A4-80 bolts. For structural applications requiring full proof load, specify A4-80 nuts (ISO 4033 or equivalent) to match the bolt grade. Always use A4 stainless washers (DIN 125) to protect the joint surface.

Sorry, this collection is empty.
Continue shopping