[object Object]Engineering Information, Conversions and Calculations

ISO DIN Plating and Surface Coatings

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

Electroplated Coatings Code System.

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
Code letterCoating metalSymbol
FNickel-chrome (1)NiCr
HCopper-nickel-chrome (1)CuNiCr
PZinc-Nickel (2)ZnNi
QZinc-Cobalt (2)ZnCo
RZinc-iron (2)ZnFe
1) Thickness of chrome layer 0,3 µm
2) Not in ISO 4042


Table 2. Minimum layer thickness (coating structure)
 Layer thickness (coating structure) in µm 
Code number1 coating metal2 coating metals
0 (1)
252+ 3
383+ 5
4124+ 8
7( 2)2510+15
8 (2)3212+18
9 (2)4016+24 (3)
1) Code number 0 applies to screw threads below M 1.6, where no specific layer thickness can be specified.
2) Does not apply to threaded components.
3) Not in ISO 4042
Table 3. Degree of gloss and after-treatment
Code letterDegree of glossChromating in accordance withSelf-color of chromate layer
DIN 50 941 Process grouppassivation by chromate
Amt (dull) (mat)none (1)none
Bmt (dull) (mat)Bbluish to bluish iridescent (2)
Cmt (dull) (mat)Cyellowish glistening to yellowish-brown,iridescent
Dmt (dull) (mat)Dolive green to olive brown
Ebk (bright)none (1)none
Fbk (bright)Bbluish to bluish iridescent (2)
Gbk (bright)Cyellowish glistening to yellowish-brown,iridescent
Hbk (bright)Dolive green to olive brown
Jgl (glossy)none (1)none
Kgl (glossy)Bbluish to bluish iridescent (2)
Lgl (glossy)Cyellowish glistening to yellowish-brown,iridescent
Mgl (glossy)Dolive green to olive brown
Nhgl (high gloss)none
Pbel (optional)B, C or D (3) at manufacturer’s discretionas for process group B, C or D
Rmt (dull) (mat)Fbrownish black to black
Sbk (bright)Fbrownish black to black
Tgl (glossy)Fbrownish black to black
Uall 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
CoatingZinc-chromatedNickelCopper nickel
Degree of glossGlossy ColorGlossy ColorGlossy ColorGlossy ColorGlossyGlossy
Nominal sizeNominal size      
< 5 mm< 3/16 "A1JA1KA1LA1TE1JG2J
5 < 10 mm3/16" < 3/8 "A2JA2KA2LA2TE2JG2J
> 10 mm> 3/8 "A3JA3KA3LA3TE3JG3J

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).

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