Stainless steel hex head bolts are externally threaded fasteners with a six-sided (hexagonal) head, manufactured entirely from stainless steel alloy. The flat hexagonal head provides six points of contact for a standard open-end wrench or socket, enabling high torque transmission during installation and removal — even in confined spaces.
Unlike carbon steel bolts, which rely on surface coatings (zinc plating, hot-dip galvanizing) for corrosion protection, stainless steel hex bolts achieve corrosion resistance through their metallurgical composition. Chromium content of at least 10.5% forms a passive oxide layer on the surface that continuously self-repairs when exposed to oxygen, making these fasteners inherently rust-resistant over their entire service life.
At Zhejiang Jiaxing Tuyue Import & Export Co., Ltd., our stainless steel fastener range covers the full spectrum of hex head bolt specifications — from M4 miniature bolts to M36 heavy-duty structural bolts — all manufactured to DIN, ISO, and ANSI standards.
Understanding each part of the bolt's geometry is critical for engineers specifying fasteners and for procurement teams verifying dimensions against drawings.
The nominal diameter (d) is the primary sizing reference, ranging from M3 to M64 in the metric system. The width across flats (s) determines wrench size. The thread length (b) varies with bolt length: partially-threaded (DIN 931 / ISO 4014) vs. fully-threaded (DIN 933 / ISO 4017) versions are both standard.
The two most common stainless steel grades for hex head bolts are SS304 (A2) and SS316 (A4). Both belong to the austenitic family — non-magnetic in their annealed state, excellent toughness at cryogenic temperatures, and inherently non-hardenable by heat treatment. But their performance diverges significantly in aggressive environments.
Composition: 18% chromium, 8% nickel (the classic "18-8" stainless). SS304 delivers good corrosion resistance in atmospheric, fresh water, and mildly acidic environments. It handles temperatures from −196 °C up to approximately 870 °C (intermittent). For the vast majority of indoor, commercial, and general-industrial applications, SS304 hex bolts offer an excellent balance of performance and cost.
Limitation: SS304 is susceptible to chloride-induced pitting corrosion. In environments with salt spray, coastal air, swimming pool chemicals, or marine splash zones, pitting can initiate at surface defects and propagate under crevices, eventually compromising structural integrity.
Composition: 16–18% chromium, 10–14% nickel, 2–3% molybdenum. The addition of molybdenum shifts the pitting resistance equivalence number (PREN) significantly higher, raising resistance to chlorides, bromides, and reducing acids. SS316 hex bolts are the standard specification for marine hardware, coastal construction, desalination plants, chemical processing, and food-grade equipment.
We also supply SS316L (low carbon variant, <0.03% C) and SS316Ti (titanium-stabilized) for specialized welded assemblies where sensitization must be avoided. Explore our full range at Stainless Steel Bolts, Nuts, Screws & Washers.
Global procurement requires precise standard alignment to ensure interchangeability and compliance. Stainless steel hex head bolts are governed by well-defined dimensional and mechanical standards.
| Standard | Thread Type | Head Type | Notes |
|---|---|---|---|
| DIN 931 | Metric (ISO thread) | Hexagonal, partial thread | Most common in Europe; shank > thread length |
| DIN 933 | Metric (ISO thread) | Hexagonal, full thread | Fully threaded; preferred for shorter bolt lengths |
| ISO 4014 | Metric (ISO thread) | Hexagonal, partial thread | International equivalent of DIN 931 |
| ISO 4017 | Metric (ISO thread) | Hexagonal, full thread | International equivalent of DIN 933 |
| ASME B18.2.1 | Unified (UNC/UNF) | Hexagonal head | US standard; uses inch dimensions |
| ASTM F593 | Unified (UNC/UNF) | Hex bolts & screws | Stainless-steel specific; covers SS304 & SS316 grades |
| BS EN ISO 4014 | Metric (ISO thread) | Hexagonal, partial thread | British Standard adopted from ISO; widely used in UK projects |
All hex head bolts supplied by Tuyue are manufactured and inspected against the applicable international standard. Mill test certificates (MTCs) conforming to EN 10204 3.1 or 3.2 are available on request.
ISO 3506 defines the property classes for stainless steel fasteners. Unlike carbon steel (where grade 8.8 or 10.9 dominates), stainless fasteners use an alphanumeric classification system.
| Property Class | Material Group | Min. Tensile Strength (Rm) | Min. Yield Strength (Rp0.2) | Min. Elongation |
|---|---|---|---|---|
| A2-50 | SS304 (soft/annealed) | 500 MPa | 210 MPa | 0.6×d (≥0.6 × diameter) |
| A2-70 | SS304 (cold worked) | 700 MPa | 450 MPa | 0.4×d |
| A2-80 | SS304 (heavily CW) | 800 MPa | 600 MPa | 0.3×d |
| A4-50 | SS316 (soft/annealed) | 500 MPa | 210 MPa | 0.6×d |
| A4-70 | SS316 (cold worked) | 700 MPa | 450 MPa | 0.4×d |
| A4-80 | SS316 (heavily CW) | 800 MPa | 600 MPa | 0.3×d |
For most international and European-destination projects, metric (ISO/DIN) thread hex bolts are standard. For North American markets and equipment manufactured to ASME/ANSI specifications, UNC (coarse thread) or UNF (fine thread) bolts are required.
Fine threads (UNF or metric fine pitch) offer greater resistance to loosening under vibration and allow finer torque adjustment, making them preferred in automotive and aerospace-adjacent applications. Coarse threads (UNC or metric standard pitch) are faster to assemble, more tolerant of minor thread damage, and generally preferred for structural and construction use.
Structural steel connections, curtain wall systems, bridge expansion joints, railing systems, and exterior cladding fixings routinely specify SS316 hex bolts where weather exposure is a concern. For interior steelwork, SS304 is typically adequate.
Boat hardware, dock fittings, offshore platform grating, and hull penetrations demand SS316 (or duplex stainless) for continuous saltwater immersion. Our ring bolts and T-bolts are also popular in marine tie-down applications.
Flanged pipe connections, heat exchanger heads, pressure vessel covers, and valve bonnets use heavy-duty hex bolts (often M20–M48) in A4-70 or A4-80 class. Hydrogen sulfide environments may require additional specification upgrades to duplex or super-duplex grades.
FDA-compliant SS316 electropolished hex bolts are standard for mixer frames, conveyor systems, filling machine frames, and cleanroom structures. Smooth, electropolished surfaces prevent bacterial harboring and simplify cleaning-in-place (CIP) procedures.
Ground-mounted and rooftop photovoltaic (PV) racking systems use hex head bolts by the thousands. We supply fasteners purpose-engineered for solar and photovoltaic module mounting. A 25-year outdoor service life with zero maintenance is the design target.
Exhaust system flanges, body panel brackets, fuel system components, and underbody structural connections all leverage stainless hex bolts where heat cycling or road salt exposure occurs.
Use this decision checklist when specifying your fastener:
Galling occurs when the micro-asperities on two stainless steel threaded surfaces weld together under the heat and pressure of assembly, causing the bolt to seize. Unlike carbon steel, stainless steel has a tenacious oxide layer that disrupts but does not eliminate galling risk. Always:
