Coating · zinc diffusion
Sherardized
A zinc diffusion coating: parts are heated in a drum with zinc powder below the melting point of zinc. The layer follows threads and edges evenly. Specified in classes by minimum thickness in EN ISO 17668.
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What it is
How Sherardized protects the joint.
01Diffusion, not a deposit on topZinc diffuses into the steel surface and forms zinc-iron layers.
02Even on threadsThe layer follows the shape of the part, including threads and edges.
03No electrolysisNo electroplating step – used for high-strength and hardened parts where hydrogen embrittlement must be avoided.
Applications
Where we use it.
01High-strength fastenersBolts and screws where electroplating is not wanted.
02Small parts in bulkProcessed in a rotating drum.
03Fine tolerancesParts where an even layer on the thread matters more than maximum thickness.
Layer thickness
Thickness, fit and threads.
Layer thickness
15 · 30 · 45µm
Classes from EN ISO 17668, by minimum local thickness. The layer adds to the outside dimensions – threads need extra clearance.
| Class (EN ISO 17668) | Minimum thickness |
|---|---|
| Class 15 | 15 µm |
| Class 30 | 30 µm |
| Class 45 | 45 µm |
How it is applied
From bare steel to coated part.
01CleanCleaning to bare steel.
02DrumParts tumble with zinc powder in a sealed, heated drum.
03DiffusionZinc diffuses into the surface below its melting point (419 °C).
04CheckLayer thickness checked against the ordered class.
FAQ
Questions we get about Sherardized.
- Sherardized or hot-dip galvanized?
- Sherardizing gives a more even layer on threads at lower process temperature; HDG is thicker.
- Which class do I need?
- Thicker classes give longer life but need more thread clearance. Tell us the environment and thread.
- Is there a hydrogen-embrittlement risk?
- Sherardizing involves no electroplating step – one reason it is chosen for hardened parts.
Next step
Quote, compare or ask.
Reviewed October 2026 by HBS Solutions. Based on EN ISO 17668. Corrosion results always belong to a complete system (pretreatment, coating, thickness) – ask us for the data sheet of the system you order.
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Compare with another coating.
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