When it comes to choosing the right threaded rod for a project, the finish matters as much as the size. BZP, HDG, and A4 stainless steel are the three most common options — and each is suited to different environments and applications. Here's a clear guide to help you choose.
BZP — Bright Zinc Plated
BZP (Bright Zinc Plated) threaded rod has a thin layer of zinc electroplated onto the surface, giving it a bright, silver-grey finish. It's the most affordable option and provides reasonable corrosion resistance for internal use and dry environments.
Where BZP falls short is outdoors or in humid conditions — the thin zinc coating can corrode relatively quickly when exposed to moisture. For anything going outside permanently, HDG or stainless is a better choice.
Best for: internal fixings, dry environments, light structural work, cost-sensitive applications.
We stock BZP threaded rod in grade 4.8 and high tensile 8.8 in sizes from M6 to M30.
HDG — Hot Dip Galvanised
HDG (Hot Dip Galvanised) rod is dipped in molten zinc, producing a much thicker coating than electroplating — typically 45–85 microns versus 5–25 for BZP. This gives it far superior corrosion resistance and makes it suitable for permanent outdoor use.
HDG is the standard choice for external construction, civil engineering, drainage, groundworks, and agricultural applications. It's considerably heavier and more durable than BZP, though the thicker coating means HDG nuts can feel stiffer to run down the thread.
Best for: external construction, structural steelwork, drainage, agricultural and civil engineering projects.
Browse our HDG threaded rod range in sizes from M8 to M24.
A4 Stainless Steel (Grade 316)
A4 stainless steel (also called 316 stainless) is a marine grade austenitic stainless steel that contains molybdenum — giving it excellent resistance to chloride corrosion and salt water. This makes it the preferred choice for marine, coastal, chemical, and food industry environments where standard galvanised rod would corrode over time.
A4 stainless is the most expensive option but offers the longest service life in harsh environments. It also has a clean, silver appearance that suits visible architectural applications.
Best for: marine and coastal environments, chemical plants, food processing, architectural ironwork, anywhere salt or acid is present.
Browse our A4 stainless threaded rod in sizes from M6 to M24.
Quick comparison
| Finish | Corrosion resistance | Best environment | Cost |
|---|---|---|---|
| BZP | Low | Internal / dry | Low |
| HDG | High | External / structural | Medium |
| A4 Stainless | Very high | Marine / chemical | High |
Need help choosing?
If you're not sure which finish to use for your project, get in touch and we'll advise. We stock metric threaded rods in all three finishes, with fast UK dispatch and free delivery on orders over £60.
