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Conversion ChartsWhat do the 'EN' and 'BS970' numbers mean?


The original 'EN' or 'Emergency Number' material designation was developed during the years of WW2 to aid the standardisation of steel reference specification and production of components produced from materials. The EN reference has continued to be used from that time - many attempts over the years have been made to update and circulate a new standard, but the original EN designation tends to remain in the workplace. The second most common material designation used in the UK is probably the BS970 standard - although officially this has been superseded by another european standard, confusingly also named the 'BS EN' number. The BS970 standard however was designed to clearly detail the carbon content and the specific type of steel via the numbers and letter given to the material (as shown below)


BS970 Specification




Steel Type:

This three digit number indicates the type of steel:

000 to 199 - Carbon manganise steel, number shows the manganise content. (x100)

200 to 240 - Free cutting steel, the 2nd and 3rd digit represents the sulphur content. (x100)

250 to 250 - Silicon manganise steel.

300 to 499 - Stainless steels and steels resistant to heat.

500 to 999 - Reserved for alloyed steels.



The single letter will be one of four designations, A, H, M or S:

A - The steel is supplied to a chemical composition as attained from a chemical batch.

H - The steel specification is 'hardenable'.

M - The material is produced to certain mechanical properties.

S - The steel is stainless in specification.


Carbon Content:

The last two numbers represent the average material carbon content. (x100)


Sometimes a further letter can be added to the designation when a certain heat treatment condition has been applied.


EN Numbers:

EN Numbers

One can only generalise the structure of the EN system without producing a chemical make-up chart that details the complete steel composition. The designations can therefore be generalised as follows:

The higher the EN number, the better the quality of steel - and the more carbon, or blended elements are added to the chemical content.

EN1 to EN3 - Low carbon, general purpose steel.

EN5 to EN16 - Medium carbon content with general purose strength.

EN19 to EN24 - Higher carbon steels with good hardenablity.

EN32 to EN36 - Hard wearing materials.

EN40 to EN45 - Spring steels.

EN56 to EN60 - Stainless steels.

It is often found that a further letter is added to the EN number to indicate a heat treated condition, more commonly used amongst the higher carbon steels to denote the hardness state.

This list should be used only as a open generalisation to aid in material selection.