Electroplated coatings
ISO : 4042 (EN ISO 4042) Electroplated coatings DIN : 267 Part 9
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 | | |
| letter | Coating metal | Symbol |
| A | Zinc | Zn |
| B | Cadmium | Cd |
| C | Copper | Cu |
| D | Brass | CuZn |
| E | Nickel | Ni |
| F | Nickel-chrome 1) | NiCr |
| G | Copper-nickel | CuNi |
| H | Copper-nickel-chrome 1) | CuNiCr |
| J | Tin | Sn |
| K | Copper-tin | CuSn |
| L | Silver | Ag |
| N | Copper-silver | CuAg |
| P | Zinc-Nickel 3) | ZnNi |
| Q | Zinc-Cobalt 3) | ZnCo |
| R | Zinc-iron 3) | ZnFe |
| 1) Thickness of chrome layer 0,3 µm | ||
| 3) Not in ISO 4042 | ||
| Table 2. Minimum layer thickness | ||
| | Layer thickness (coating structure) in µm | |
| Code number | 1 coating metal | 2 coating metals |
| 0 1) | – | – |
| 1 | 3 | – |
| 2 | 5 | 2+ 3 |
| 3 | 8 | 3+ 5 |
| 4 | 12 | 4+ 8 |
| 5 | 15 | 5+10 |
| 6 | 20 | 8+12 |
| 7 2) | 25 | 10+15 |
| 8 2) | 32 | 12+18 |
| 9 2) | 40 | 16+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 | |||
| Codeletter | 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) In the case of Zn and Cd however, process group A | 2) 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 | |||||||
| | | | | | | | Copper |
| | Coating | | Zinc-chromated | | | Nickel | nickel |
| | Degree of gloss | Glossy | Glossy | Glossy | Glossy | Glossy | Glossy |
| Nominal size | Nominal size | Color | Color | Color | Color | | |
| metric | inch | none | bluish | yellowish | black | – | – |
| < 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).
