MARYLAND METRICS: Technical Data Chart

ISO : 4042 (EN ISO 4042) Electroplated coatings
DIN : 267 Part 9

Electroplated coatings/Rivestimenti elettrolitici/Revêtement électrolytiques/
Revestimientos electrolìticos/Elektrolytische Überzüge

Code system/Sistema di codifica/Systême de codification/sistema de codificaciòn/Kodifizierungssystem

1. Scope and field of application
These technical conditions are in particular related to threaded fasteners (mainly bolts and nuts), but are also applicable
to the whole range of mechanical fasteners.

2. Electroplated coatings
An electrolytically applied coating shall be defined as a protective metallic layer being deposited onto the surface of metal articles by immersing these parts in an aqueous solution through which an electrical current is passed.

Note: The use of the nomenclature “galvanizing” for this treatment is not correct.
This information on electroplated coatings corresponds with DIN 267 Part 9 and ISO 4042.

3. Code system
The electroplated coatings of mechanical fasteners are designated by a code consisting of a combination of two capital letters and a number.
This callout system is built up as follows:
– a capital letter for the coating metal (Table 1)
– a number for the minimum layer thickness (coating structure) (Table 2)
– a capital letter for the degree of gloss and after-treatment (Table 3)

Table 1. Coating metal   Table 2. Minimum layer thickness (coating structure)
        Layer thickness (coating structure) in µm  
Code letter Coating metal Symbol   Code number 1 coating metal 2 coating metals
A Zinc Zn   0 1)
B Cadmium Cd   1 3
C Copper Cu   2 5 2+ 3
D Brass CuZn   3 8 3+ 5
E Nickel Ni   4 12 4+ 8
F Nickel-chrome 1) NiCr   5 15 5+10
G Copper-nickel CuNi   6 20 8+12
H Copper-nickel-chrome 1) CuNiCr   7 2) 25 10+15
J Tin Sn   8 2) 32 12+18
K Copper-tin CuSn   9 2) 40 16+24 3)
L Silver Ag   1) Code number 0 applies to screw threads below
N Copper-silver CuAg   M 1.6, where no specific layer thickness can be specified.
P Zinc-Nickel 3) ZnNi   2) Does not apply to threaded components.
Q Zinc-Cobalt 3) ZnCo   3) Not in ISO 4042
R Zinc-iron 3) ZnFe    
1) Thickness of chrome layer 0,3 µm    
3) Not in ISO 4042    

Table 3. Degree of gloss and after-treatment
Code letter Degree of gloss Chromating in accordance with
DIN 50 941 Process group
Self-color of chromate layer
passivation by chromate
A mt (dull) (mat) none 1) none
B mt (dull) (mat) B bluish to bluish iridescent 2)
C mt (dull) (mat) C yellowish glistening to yellowish-brown,iridescent
D mt (dull) (mat) D olive green to olive brown
E bk (bright) none 1) none
F bk (bright) B bluish to bluish iridescent 2)
G bk (bright) C yellowish glistening to yellowish-brown,iridescent
H bk (bright) D olive green to olive brown
J gl (glossy) none 1) none
K gl (glossy) B bluish to bluish iridescent 2)
L gl (glossy) C yellowish glistening to yellowish-brown,iridescent
M gl (glossy) D olive green to olive brown
N hgl (high gloss) none
P bel (optional) B, C or D 3) at manufacturer’s discretion as for process group B, C or D
R mt (dull) (mat) F brownish black to black
S bk (bright) F brownish black to black
T gl (glossy) F brownish black to black
U all finishes   no chromate treatment
1) Passivation treatments are possible only with zinc or cadmium coatings.
2) However, process group A Only applies to Zn coatings
3) Process groups B, C or D in accordance with DIN 50 941 only apply to cadmium and zinc coatings.
In the case of other electroplated coatings, "P" in the code symbol signifies "degree of gloss optional".

Ordering code for electroplated coatings for commercial fasteners
Coating Zinc-chromated Nickel Copper nickel
Degree of gloss Glossy Color
Glossy Color
Glossy Color
Glossy Color
Glossy Glossy
Nominal size Nominal size            
metric inch        
< 5 mm < 3/16 " A1J A1K A1L A1T E1J G2J
5 < 10 mm 3/16" < 3/8 " A2J A2K A2L A2T E2J G2J
> 10 mm > 3/8 " A3J A3K A3L A3T E3J G3J

Example of coding: A3L means zinc-plating (A in Table 1) with a minimum layer thickness of 8 µm
(3 in Table 2) and yellow-chromated with a glossy degree of gloss (L in Table 3).
Callout Example: Hexagon bolt DIN 931 - M12 x 50 - 8.8 - A3L.

Chromate (passivate) effected immediately after electroplating by short immersing in chromic acid
solutions. The chromating process increases the corrosion protection and prevents a starting and
a discolouring of the zinc layer. The protective effect of the chromate layer is different depending
upon group of procedures (see table).

Click for: (Ref. ISO 4092) Plating thicknesses for threaded metric fasteners

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