Buyer guide
Prepared by LD Screw · Reviewed · Practical guidance for fastener RFQ preparation.
A2 and A4 describe stainless fastener material groups used in fastener standards, while 304 and 316 are familiar alloy-family references used in many purchasing conversations. They are helpful starting points, but they should not be treated as automatically identical designations across every material standard. Confirm the exact grade, fastener property class and governing standard for the order.
Practical comparison for buyers
Material selection depends on the real exposure, expected service life, cleaning conditions, temperature, mating materials and project specification. Stainless steel is corrosion resistant, but no grade is universally corrosion proof.
| Purchasing direction | Common starting point | What to verify |
|---|---|---|
| A2 / 304 family | General indoor, clean outdoor and many industrial uses | Exact grade, moisture, chemicals, temperature and appearance requirements |
| A4 / 316 family | Applications needing improved resistance in chloride-related or more demanding exposure | Chloride level, immersion, crevices, cleaning and project approval |
| A2-70 or A4-70 | A stainless material group combined with a fastener property class | Product standard, diameter range, mechanical requirement and test documents |
| Special stainless grade | Project-specific corrosion, temperature or strength need | Full material designation, approved equivalents and certification requirement |
Alloy grade and property class are separate
A request for 316 stainless does not by itself define the bolt dimensions or mechanical class. Likewise, A4-70 does not define the head style, length, thread coverage or surface condition. The RFQ should combine the dimensional standard with the stainless designation and the required property class.
Nuts and washers should also be specified for compatibility. Do not assume that every component in a set has the same material, strength or verification requirement unless the purchase specification states it.
- State the product standard or attach the drawing
- Name the exact stainless designation and permitted equivalents
- Add the property class, size, pitch and thread tolerance
- List certificate, test and marking requirements before quotation
Corrosion, contamination and galling
Corrosion performance is affected by surface condition, fabrication contamination, stagnant moisture, crevices and contact with other metals. A4 is often selected for improved resistance in chloride-related conditions, but the actual environment still has to be reviewed.
Stainless threaded assemblies can gall during installation. Suitable thread condition, cleanliness, compatible lubrication and controlled installation practice may be relevant to the buyer application. These details should be agreed when assembly performance is critical.
- Describe the exposure instead of asking only for rust-proof fasteners
- Confirm passivation or surface-cleanliness requirements when applicable
- Identify dissimilar metals and electrically conductive environments
- State installation, lubrication or anti-galling requirements if controlled
What to send with a stainless fastener RFQ
Send the standard or drawing, exact size, stainless designation, property class, quantity, surface condition, service environment and required documentation. If a project specification names an approved grade or standard, attach that requirement and identify whether alternatives may be reviewed.
- Fastener type, standard, diameter, pitch and length
- A2, A4 or complete material designation and required property class
- Exposure, temperature, mating parts and expected surface condition
- Quantity, certificates, inspection, labels and export packing