Coatings and Finishes Overview
A coating slows corrosion, changes appearance and changes friction, which changes the torque needed. It never changes the grade.
Common finishes
| Finish | Thickness (typical) | Best for | Watch out |
|---|---|---|---|
| Plain / oil | None | Indoor, painted later | Rusts |
| Zinc plate (F1941) | 5 - 8 micrometres | Indoor, mild | Hydrogen embrittlement on hard parts |
| Hot-dip galvanized (F2329) | 50+ micrometres | Outdoor structural | Oversize nuts; not A490 |
| Mechanical zinc (B695) | By class | Structural, hard parts | Matte appearance |
| Zinc flake (F3393) | 6 - 12 micrometres | Automotive, A490 | Thin; coating damage |
| Black oxide | Very thin | Appearance, sockets | Little corrosion protection |
These tables carry the same figures as the printed sheet below.
The printed sheet
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Coatings and finishes overview
What it is
FIELD IDENTIFICATION
A coating slows corrosion, changes appearance and changes friction, which changes the torque
needed. It never changes the grade.
ZINC
YELLOW
GALV
BLACK
Finish is chosen for corrosion, friction and
appearance
Common finishes
Finish
Thickness (typical)
Best for
Watch out
Plain / oil
None
Indoor, painted later
Rusts
Zinc plate (F1941)
5 - 8 micrometres
Indoor, mild
Hydrogen embrittlement on hard parts
Hot-dip galvanized (F2329)
50+ micrometres
Outdoor structural
Oversize nuts; not A490
Mechanical zinc (B695)
By class
Structural, hard parts
Matte appearance
Zinc flake (F3393)
6 - 12 micrometres
Automotive, A490
Thin; coating damage
Black oxide
Very thin
Appearance, sockets
Little corrosion protection
Key points
Hydrogen embrittlement risk rises sharply above about HRC 39: Grade 8, 10.9, 12.9, A490, A574.
Governing standards: ASTM F1941/F1941M-16(2025); ASTM F2329/F2329M-15(2023); ASTM B695-21; ASTM F3393-24; ISO 4042:2022; ISO 10684:2004; ISO 10683:2018.
Editions shown are the latest confirmed as of September 2026. The drawing and the governing standard always take precedence over this sheet.
torquing any fastener. Verify the current governing standard, project documents, OEM requirements, size, thread, coating and lot certification. To the fullest extent permitted by law, The Fastener App disclaims liability
arising from reliance on this reference.
Fastener Guide reference FG-C32142 · thefastenerapp.com/fastener-guide/technical-reference/coatings-and-finishes-overview · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.
