Stainless steel hex bolts are widely specified for construction, machinery, HVAC, MEP, food equipment, outdoor assemblies and industrial projects where corrosion resistance and a clean finish matter. A reliable purchase requires more than choosing a diameter and length: buyers should confirm the stainless grade, property class, thread standard, head dimensions, mating nuts and washers, surface condition and inspection documents.
What Is a Stainless Steel Hex Bolt?
A stainless steel hex bolt has an external hexagonal head designed for installation with a wrench or socket. It may be fully threaded or partially threaded depending on the standard, length and application. Fully threaded versions provide adjustment along most of the shank, while partial-thread bolts leave an unthreaded grip that may be preferred where shear planes or alignment are important.
Hex bolts are commonly assembled with a compatible hex nut, flat washer and, when the joint design calls for it, a locking element. The complete joint should be selected as a system rather than treating the bolt alone as the finished connection.
A2-70 Marking Explained
One of the supplied photographs clearly shows an A2-70 head marking. Under the applicable ISO 3506-1 system, A2 identifies an austenitic stainless-steel group commonly associated with 304-type stainless steel, while property class 70 typically indicates a minimum tensile strength of 700 MPa within the standard’s applicable conditions. The marking is useful for identification, but critical orders should still be supported by the required material certificate, mechanical test report and dimensional inspection.
A head marking on one photographed sample must not be assumed to describe every stainless bolt in an order. Buyers should state the exact grade and property class on the purchase specification and confirm that the required marking, traceability and certification will be supplied.
304 vs 316 Stainless Steel Hex Bolts
| Common designation | Typical use | Selection note |
|---|---|---|
| A2 / 304 | Indoor equipment, general outdoor construction, machinery and many industrial assemblies | Good general corrosion resistance and widely available |
| A4 / 316 | Coastal, marine, chloride-exposed and more aggressive environments | Molybdenum improves resistance to chloride pitting |
| 316L | Fabricated or welded assemblies with low-carbon requirements | Project specifications may require separate material and welding controls |
Neither 304 nor 316 is universally correct. Exposure to chlorides, acids, cleaning chemicals, high temperatures or dissimilar metals can change the required alloy. Stainless steel is corrosion resistant, not corrosion proof, so the actual service environment and the engineer’s specification should guide the decision.
DIN 933, ISO 4017 and Thread Options
Fully threaded metric hex head screws are frequently requested as DIN 933 or ISO 4017. DIN 933 is a familiar legacy reference, while ISO 4017 is the current international reference used for many new specifications. They are often treated as commercial equivalents, but buyers should not assume every dimension, tolerance or technical requirement is identical. State the required standard on the enquiry and check the approved drawing or standard edition before substitution.
- Metric coarse thread: the most common choice for general fastening and broad availability.
- Metric fine thread: may be specified for adjustment, limited engagement or particular joint requirements.
- Imperial thread: UNC, UNF or another system should be clearly stated for North American and equipment-replacement orders.
- Full or partial thread: confirm the grip length and thread engagement required by the assembly.
Bolts, Nuts and Washers as an Assembly
The second product image shows stainless bolts assembled with hex nuts, flat washers and spring washers. Flat washers distribute bearing pressure and protect the contact surface. Spring washers may be supplied when specified, but their suitability depends on the joint design, vibration conditions and governing standard. For safety-critical joints, the locking method must be selected and validated by the project engineer.
Matching material and compatible strength are important. Combining stainless bolts with unsuitable nuts or dissimilar metals can create galling, corrosion or inconsistent preload. Buyers should specify whether nuts and washers must be A2, A4, another alloy or a certified matched set.
How to Specify Stainless Hex Bolts
- Standard: DIN 933, ISO 4017, DIN 931, ISO 4014 or another required specification.
- Thread: metric or imperial diameter, pitch and tolerance.
- Length: measured from under the head to the end for a standard hex bolt.
- Thread coverage: full thread or the required unthreaded grip length.
- Material: A2/304, A4/316 or another specified stainless grade.
- Property class: such as 50, 70 or 80 when applicable and required.
- Accessories: nuts, flat washers, spring washers or other locking components.
- Documentation: material certificates, mechanical testing, dimensional reports and marking requirements.
- Quantity and packing: pieces per box, pallet method, labels and export requirements.
Preventing Stainless Thread Galling
Austenitic stainless threads can gall or seize during tightening, especially at high speed, under heavy preload or when both mating surfaces are dry. Common controls include clean threads, compatible nuts, suitable anti-seize lubricant, slower installation speed and controlled tightening. Lubrication changes the relationship between torque and preload, so torque values must be adjusted for the actual joint and lubricant rather than copied from a generic chart.
Quality Inspection for Bulk Orders
- Confirm grade, property class and certificate requirements.
- Inspect head marking, head dimensions and wrench fit.
- Check diameter, pitch and thread acceptance with suitable gauges.
- Measure length, thread length and straightness.
- Review the surface for contamination, burrs, cracks or damaging tool marks.
- Test the fit of matching nuts and verify the supplied washer dimensions.
- Confirm lot identification, count, labels and export packing.
Passivation or other cleaning requirements should be agreed before production. A bright appearance alone does not prove the stainless grade or mechanical property class; traceable records and testing are the appropriate evidence for controlled projects.
Applications
- Construction, façade supports and outdoor structures
- HVAC, MEP, pipe supports and cable-management systems
- Machinery, guards, frames and equipment assembly
- Food-processing and clean industrial equipment
- Marine and coastal projects when the specified alloy is suitable
- Solar mounting, water treatment and general infrastructure
Standard Sizes, Custom Production and Bulk Supply
SHENHUI supplies stainless steel hex bolts for distributors, importers, contractors, equipment manufacturers and industrial projects. Standard metric sizes can be quoted for wholesale orders, while custom length, thread coverage, grade, marking and packaging can be reviewed from a drawing or approved sample. Related bolt products, nuts, washers and OEM fastener services are also available.
Frequently Asked Questions
What does A2-70 mean on a stainless steel bolt?
A2 identifies an austenitic stainless group commonly associated with 304-type stainless, and property class 70 typically corresponds to a 700 MPa minimum tensile strength under the applicable ISO 3506-1 conditions. Confirm the standard, diameter range and certification for the actual order.
Should I choose 304 or 316 stainless hex bolts?
304 is widely used for general service. 316 is often selected for coastal, marine or chloride exposure. The final choice must consider chemicals, temperature, crevices, dissimilar metals and the project specification.
Are DIN 933 and ISO 4017 exactly the same?
They are commonly cross-referenced for fully threaded metric hex head fasteners, but buyers should not assume every technical detail is identical. Specify the required standard and approve any substitution.
Can nuts and washers be supplied with the bolts?
Yes. Matching stainless hex nuts, flat washers and other specified accessories can be packed as sets when the material, dimensions and quantity are included in the enquiry.
Can SHENHUI manufacture custom stainless bolts?
Yes. Custom length, thread coverage, grade, marking and packing can be quoted from a confirmed drawing or sample, subject to technical review and order quantity.
Request a Quotation
Send the standard, thread size, length, stainless grade, property class, required nuts and washers, quantity, destination and certificate requirements. Contact SHENHUI Fasteners for a stainless steel hex bolt bulk or custom quotation.