Product Overview
Put carbon or alloy bolting into salt air, process chemicals or daily washdown and it will corrode - the joint seizes, the studs have to be cut out, and the maintenance bill outlives the parts. ASTM A193 B8M is the 316 stainless grade of A193 bolting, and it's the grade most specifications name where corrosion resistance matters more than raw strength.
We supply B8M stud bolts from 1/2" to 4", normally as fully threaded studs cut to length so you can set the length your joint actually needs. Threads are UNC or 8UN, the finish is passivated, and the studs are supplied to match ASTM A194 8M heavy hex nuts. Both Class 1 and Class 2 are available - Class 2 is strain hardened for higher strength, per ASTM A193 B8M.
Kennen Steel International Co., Ltd. is a China-based steel trading company and a first-tier mill agent. We don't run a factory - we buy direct from vetted source mills, hold them to the specification you agree, and manage the export side end to end. Three decades of steel trading in China and a vetted network of source mills is what stands behind every order.
Typical shipments go to marine and offshore contractors, chemical and petrochemical plants, water and wastewater projects, and food and pharmaceutical equipment builders - buyers who need the right grade, a matched nut, clean threads and paperwork that clears the gate.
Key Advantages
Direct mill supply, not a resold catalogue
We buy from the mills and we inspect what they make. The grade stamped on the stud is the grade in the box, and if a batch doesn't meet the agreed specification it doesn't ship. You get mill quality with someone accountable for the order.
B8M and 8M supplied as a matched set
Studs and nuts are a system, not two separate purchases. We supply B8M studs with matching ASTM A194 8M nuts so the joint is correct from the start - the right grade on both sides, and no chasing hardware after the studs arrive.
316 stainless where carbon bolting corrodes
The molybdenum in 316 is what separates B8M from plain 18-8 stainless (B8, the 304 grade). It's the difference between bolting that survives a marine atmosphere or a chemical plant and bolting that pits, gall and seizes. Where the service is aggressive, B8M is usually the grade written into the spec.
Class 1 or Class 2, to match the joint
Class 1 is carbide solution treated; Class 2 adds a strain-hardening step for higher strength, per ASTM A193 B8M. If your joint design calls for the stronger class - or the spec simply says B8M Class 2 - tell us and we'll supply it.
Imperial sizes, UNC and 8UN threads
Inch sizes dominate this grade. We cover 1/2" through 4", with 8UN where the larger imperial sizes call for it and UNC for the everyday range. Send us the line spec and we'll supply the thread series it assumes.
Passivated, and honest about coatings
B8M studs are supplied passivated so the surface is clean and the natural oxide layer does its job. Note that B8M is not normally hot-dip galvanized - that's a treatment for carbon and alloy bolting, not for stainless; if you need a coated or anti-seize variant, tell us the service and we'll confirm what's available rather than assume.
Documents that clear the gate
An EN 10204 3.1 mill test certificate per batch comes as standard, dimensional inspection is run to the cited standard, third-party inspection can be arranged on request, and we support the destination conformity paperwork some markets require, such as KEBS or PVoC.
Technical Specifications
| Item | Specification |
|---|---|
| Product Name | B8M Stud Bolts (316 stainless steel stud bolts with A194 8M nuts) |
| Standard | ASTM A193 B8M (stud bolts); matching nuts to ASTM A194 8M; dimensions per ASME B18.2.2 as applicable |
| Material | AISI 316 stainless steel |
| Grade / Class | B8M, Class 1 (carbide solution treated) and Class 2 (carbide solution treated plus strain hardened, per ASTM A193 B8M) |
| Size Range | 1/2"–4" (M12–M100) |
| Length | Cut to order |
| Stud Form | Fully threaded stud, normally; other forms confirmed per order |
| Thread Series | UNC as standard; 8UN for larger imperial sizes as specified |
| Mechanical Properties | Per ASTM A193 B8M, Class 1 or Class 2; actual figures confirmed per heat on the mill test certificate |
| Hardness | Per ASTM A193 B8M; the specified limit is confirmed per batch on the mill test certificate |
| Service Temperature | Suitability confirmed against ASTM A193 B8M and your joint design; the recommended limit is confirmed per application |
| Corrosion Resistance | 316 (molybdenum-bearing) stainless, intended for marine, chemical and general corrosive service; performance in a specific medium is confirmed per application |
| Finish | Passivated. B8M is not normally hot-dip galvanized; other coatings or anti-seize treatment confirmed per order |
| Matching Nuts | ASTM A194 8M |
| Marking | Grade and heat / lot marking per the cited standard; confirmed per order |
| Dimensional Tolerance | In accordance with the cited standard; confirmed per size |
| Packing | Wooden cases or drums with protective lining, strapped for export |
| Certificate | EN 10204 3.1 mill test certificate per batch |
Class, thread series, length, finish and packing are confirmed against your specification and destination before the order is placed.
Step-by-Step Manufacturing Process
- Bar selection - 316 stainless round bar is inspected and cut to the stud length. The molybdenum content of the bar is what makes the finished stud a B8M and not a plain 18-8 grade.
- End preparation - ends are chamfered so the nut starts cleanly and no burr is left to gall the thread.
- Thread rolling - threads are rolled rather than cut. Rolling keeps the grain flow continuous through the thread, and on stainless, which work-hardens, a rolled thread is both stronger and cleaner than a cut one.
- Carbide solution treatment - the stud is solution treated to dissolve carbides and restore corrosion resistance. This is the treatment that defines Class 1.
- Strain hardening (Class 2) - where Class 2 is specified, an additional strain-hardening step raises the strength, per ASTM A193 B8M.
- Passivation - acid passivation removes free iron and surface contamination and lets the natural chromium oxide layer re-form, which is what actually protects the stud.
- Testing and marking - mechanical and hardness tests are run on samples from the batch, and the studs are marked with grade and lot before the batch certificate is raised.
- Packing - studs and matching 8M nuts are packed with protective lining into wooden cases or drums, isolated from carbon steel to avoid iron contamination, and strapped for export.
Quality Assurance & Certificates
- EN 10204 3.1 mill test certificate per batch - chemistry, mechanical properties and hardness
- Dimensional inspection against the cited standard (ASTM A193 B8M)
- Thread gauging per size and series (UNC / 8UN)
- Passivation check and visual inspection for surface contamination
- Third-party inspection available on request (SGS, BV, Intertek)
- Documentation support for destination conformity schemes (for example KEBS or PVoC)
- Every shipment is checked against the agreed specification before it leaves, so what lands matches what was ordered
Core Applications
- Flanged joints in chemical and petrochemical plants
- Offshore platforms, marine structures and shipboard piping
- Water treatment and desalination plants
- Food, beverage and pharmaceutical process equipment
- Pulp and paper, and other wet, mildly corrosive process lines
- Heat exchangers, tanks and vessels where stainless bolting is specified
- MRO distributor stock and plant maintenance programmes
FAQ
What's the difference between B8 and B8M?
B8 is the 304 grade of A193 stainless bolting; B8M is the 316 grade, with molybdenum added for better resistance to chlorides and chemical attack. Where the service is marine, chemical or otherwise aggressive, the spec usually says B8M. If your requirement is plain 304, we can supply B8 as a related variant - tell us the service and we'll confirm.
Class 1 or Class 2 - which do I need?
Class 1 is carbide solution treated. Class 2 is carbide solution treated plus strain hardened, which gives higher strength, per ASTM A193 B8M. Which one applies is a design decision from your joint calculation or piping spec, not a preference - send us the spec and we'll supply the class it calls out.
Do the studs come with nuts?
Yes. B8M studs ship with matching ASTM A194 8M nuts, so the joint is correct from the start and you're not sourcing hardware separately.
Why aren't B8M studs hot-dip galvanized?
Hot-dip galvanizing is a protective treatment for carbon and alloy steel, not for stainless - the zinc adds nothing to a 316 stud and the process can affect the surface. B8M is supplied passivated. If your service needs a coating or anti-seize treatment, tell us the environment and we'll confirm what's available.
Which thread series should I use, UNC or 8UN?
UNC is the everyday imperial series; 8UN is common on larger sizes and where the piping or equipment spec calls for it. It's a spec decision - send us the line specification and we'll supply the series it assumes.
What are the mechanical properties?
B8M follows ASTM A193 B8M, with Class 2 higher strength than Class 1. The actual figures for your heat - tensile, yield, elongation and hardness - are stated on the mill test certificate. We quote the certificate, not a brochure number.
Can B8M be used at high temperature?
Stainless bolting behaves differently from chrome-moly grades at elevated temperature, and the limit depends on the class, the joint and the service. Suitability is confirmed against ASTM A193 B8M and your joint design for the application - if your joint runs hot, tell us the temperature and we'll confirm before you commit.
Do you provide test certificates and inspection?
Yes. Every batch ships with an EN 10204 3.1 mill test certificate covering the agreed details. Third-party inspection (SGS, BV, Intertek) can be arranged on request, and we can support destination conformity documentation such as KEBS or PVoC where your market requires it.
Can you supply non-standard lengths or a specific thread form?
Yes - stud lengths are cut to order. Send us the size, thread series and stud form from your specification and we'll confirm before you commit.
Are you the manufacturer?
No. We're a China-based steel trading company and a first-tier mill agent. We buy direct from vetted source mills, verify grade and dimensions, and manage the export - passivation, packing, certificates and shipping. You get mill quality with someone accountable for the order.
