Why One Steel Has Five Different Names
Steel grades were named by whoever standardised them, and the standards bodies did not coordinate. Britain wrote BS 970. Germany wrote DIN and assigned Werkstoff numbers. The Americans wrote AISI and SAE. Europe later wrote the EN standards, which gave the same steels composition-based names of their own. None of these replaced the others in practice, because the designations outlived the documents: BS 970 is withdrawn and UK industry still orders EN19 by name.
The practical consequence is that a buyer reads a drawing in one system and a certificate in another. A European drawing calls up 42CrMo4; the mill certificate from a UK stockholder says 708M40; the customer in Texas specifies 4140. All three are the same chromium-molybdenum steel.
The useful part: four of the five systems put the carbon content in the designation, and they all express it the same way — hundredths of a percent. Once you know where to look in each format, you can read the approximate carbon off any of them without a table.
BS 970: What the Six Characters Mean
The BS 970:1991 designation is the one UK certificates use, and it is the most informative of the five. It is always three digits, then a letter, then two digits — 817M40, 080M40, 535A99.
The Steel Family
The first three digits place the steel in a group. 000–199 are the carbon and carbon-manganese steels, and here the number also tracks the manganese content — 070M55 and 080M40 carry roughly 0.70% and 0.80% manganese respectively. 200–240 are the free-cutting steels, which is where EN1A's 230M07 sits. 300–499 cover stainless and heat-resisting grades. 500–999 are the alloy steels — every alloy grade Parkside stocks falls in this band, from 535A99 through to 835M30.
How It Was Bought
The letter is the part most often misread. It says nothing about the steel's composition — it records which property the supplier guaranteed when the bar was made. A means supplied to a chemical analysis. M means supplied to mechanical properties, so tensile and yield were the acceptance criteria. H means supplied to hardenability. S denotes stainless. Two bars of near-identical composition can carry different letters because they were ordered against different tests.
The Carbon Content
The last two digits give the carbon content in hundredths of a percent. 817M40 is a 0.40% carbon steel; 535A99 is a 0.99% carbon steel; 655M13 is 0.13%. This is the single most useful thing in the designation, because carbon is what sets the hardenability and the strength ceiling — and because, as the next system shows, the European and American names put the same figure in the same units.
Check it yourself: the table below decodes every stocked grade against the composition Parkside publishes for it.
Every Stocked Grade, Decoded
Each row takes the BS 970 number apart and sets the carbon it implies against the carbon Parkside actually publishes for that grade on the grade equivalents table. The rule lands within 0.01% for 17 of the 19 grades. Two values are flagged amber: EN31's 535A99 is 0.015 out, and EN1A's 230M07 reads 0.07% against a specified 0.07–0.15% band — the designation has taken the bottom of the range rather than its middle.
| BS 970 | Known as | Group | Letter | Carbon implied | Carbon published |
|---|---|---|---|---|---|
| 230M07 | EN1A | 230 | M (mechanical) | 0.07% | 0.11% |
| 070M20 | EN3B | 070 | M (mechanical) | 0.20% | 0.20% |
| 080M40 | EN8 | 080 | M (mechanical) | 0.40% | 0.40% |
| 605M36 | EN16 | 605 | M (mechanical) | 0.36% | 0.35% |
| 708M40 | EN19 | 708 | M (mechanical) | 0.40% | 0.40% |
| 817M40 | EN24 | 817 | M (mechanical) | 0.40% | 0.40% |
| 655M13 | EN36 / EN36B | 655 | M (mechanical) | 0.13% | 0.12% |
| 722M24 | EN40B | 722 | M (mechanical) | 0.24% | 0.24% |
| 070M55 | EN9 | 070 | M (mechanical) | 0.55% | 0.55% |
| 805M20 | 8620 / EN362 | 805 | M (mechanical) | 0.20% | 0.21% |
| 210M15 | EN32M | 210 | M (mechanical) | 0.15% | 0.15% |
| 080A42 | EN8D | 080 | A (analysis) | 0.42% | 0.43% |
| 212A42 | EN8M / 212A42 | 212 | A (analysis) | 0.42% | 0.42% |
| 832M13 | EN36C | 832 | M (mechanical) | 0.13% | 0.13% |
| 835M15 | EN39B | 835 | M (mechanical) | 0.15% | 0.15% |
| 535A99 | EN31 | 535 | A (analysis) | 0.99% | 0.98% |
| 826M40 | EN26 | 826 | M (mechanical) | 0.40% | 0.40% |
| 835M30 | EN30B | 835 | M (mechanical) | 0.30% | 0.30% |
| 080A15 | BMS | 080 | A (analysis) | 0.15% | 0.15% |
EN Numbers: Old British “En” Versus European EN
This is the designation that causes the most confusion on this site's enquiry line, and the confusion is entirely reasonable: two unrelated systems ended up sharing two letters.
⚠ EN19 and BS EN 10083 have nothing to do with each other. EN19 is a grade — one specific chromium-molybdenum steel. BS EN 10083 is a standard document covering a family of quenched and tempered steels. The first is a steel; the second is the specification you buy it to.
The British En numbers — En8, En19, En24, En36 — are a legacy series. They were introduced in 1941, in a war emergency schedule of British Standards that was later carried into BS 970. The letters are commonly said to stand for “Emergency Number”, and that reading fits the origin, but it is a repeated story rather than a documented expansion — worth knowing as an explanation, not quoting as a fact. They are sequential catalogue references and, unlike every other system on this page, they encode nothing at all. There is no sense in which En24 is three more of something than En21. The number is an index, and you must look it up. BS 970 is withdrawn and the En numbers are no longer current, yet UK industry still orders by them, which is why Parkside's stock list is written in both.
The European EN grade names are the opposite — densely informative. 42CrMo4 reads as: 42 hundredths of a percent carbon, chromium and molybdenum as the alloying elements, and a trailing figure giving the content of the first-named element divided by a fixed factor, which is 4 for chromium. That predicts about 1.0% chromium, and Parkside's published range for the grade is 0.90–1.20%. The same arithmetic on 100Cr6 gives 1.00% carbon and 1.5% chromium, against published figures of 0.93–1.05% and 1.35–1.65%.
Where the arithmetic stops helping: when a name carries several alloying elements, the trailing numbers do not map cleanly onto each one, and different elements use different divisors. Read the carbon from the front with confidence; for anything past that, use the cross-reference rather than the name.
DIN and the Werkstoff Number
German drawings and most European certificates carry a Werkstoff number: a single digit, a decimal point, then four more digits. EN19 is 1.7225. EN24 is 1.6582. EN31 is 1.3505.
The leading digit is the material class, and it is the only part that is reliably readable: 1 is steel. It is worth knowing that the class digit genuinely discriminates — the cast irons Parkside stocks are not 1.x at all but 0.6025 for grey iron and 0.7040, 0.7050 and 0.7060 for the ductile grades. The two digits after the point place the grade in a steel group, and the final pair are sequential within it.
⚠ Do not try to read composition out of a Werkstoff number. It is a catalogue index with a class prefix, not a description. Nothing in 1.7225 tells you it is a 0.42% carbon chromium-molybdenum steel. If a drawing gives you only a Werkstoff number, convert it to a name before you try to reason about the steel.
AISI and SAE Four-Digit Numbers
American drawings use a four-digit number, and it splits cleanly in two. The first two digits identify the alloy family — 10xx plain carbon, 41xx chromium-molybdenum, 43xx nickel-chromium-molybdenum, 86xx the nickel-chromium-molybdenum case hardening series. The last two give the carbon content in hundredths of a percent, exactly as BS 970 does.
That shared convention is the most practical thing on this page. AISI 4140 and 708M40 are the same steel and both end in 40 for the same reason. AISI 1020 is 070M20. AISI 1055 is 070M55. SAE 8620 is 805M20 — and the 20 agrees even though the leading digits do not correspond at all.
AISI and SAE numbering are effectively interchangeable for engineering bar; the grades Parkside stocks appear in the equivalents table under whichever of the two is in common use for that steel.
Reading a Designation Off a Drawing or Certificate
Identify the system first — the shape of the designation gives it away before you know anything about the steel:
| If it looks like… | It is | Example | What you can read straight off |
|---|---|---|---|
| 3 digits, letter, 2 digits | BS 970 | 817M40 | Family, how it was bought, and carbon — all three |
| Digit, point, 4 digits | Werkstoff | 1.6582 | Material class only. Steel if it starts with 1 |
| 4 bare digits | AISI / SAE | 4340 | Alloy family and carbon |
| Number + element symbols | European EN name | 34CrNiMo6 | Carbon, and which elements are deliberate |
| “EN” + 1 or 2 digits | Old British En series | EN24 | Nothing — it is an index. Look it up |
| “EN” + 5 digits | A European standard, not a grade | EN 10083 | The specification, not the steel |
On a mill certificate the designation sits alongside the cast number and the measured composition, so you can check the reading against the analysis directly: if the last two digits of a BS 970 number disagree with the certificate's carbon by more than a hundredth or so, look twice at which grade you have been sent. Certificates issued to BS EN 10204 are covered on Parkside's accreditations and quality page, and the elements themselves are explained in the chemical elements guide.
Where to Find the Equivalent Across All Five Systems
Reading a designation tells you roughly what the steel is. Finding its counterpart in another system is a lookup, and Parkside publishes the full table at grade equivalents. Five of the most commonly cross-referenced grades:
| Known as | BS 970 | European name | Werkstoff | AISI / SAE |
|---|---|---|---|---|
| EN8 | 080M40 | C40 | 1.0511 | AISI 1040 |
| EN19 | 708M40 | 42CrMo4 | 1.7225 | AISI 4140 |
| EN24 | 817M40 | 34CrNiMo6 | 1.6582 | AISI 4340 |
| EN31 | 535A99 | 100Cr6 | 1.3505 | AISI 52100 |
| 8620 / EN362 | 805M20 | 20NiCrMo2-2 | 1.6523 | SAE 8620 |
⚠ Equivalents are near-equivalents. EN24 is 817M40 and 34CrNiMo6 — one designation implies 0.40% carbon and the other 0.34%. Both are right for their own standard, because the two specifications draw slightly different bands around the same steel. For general engineering they interchange; where a specification is tight, work from the certificate rather than the equivalence.
Individual terms are defined in the steel terminology glossary. The two grades used as worked examples throughout this page have full data sheets: EN24 (817M40) and EN1A (230M07). If a drawing has arrived with a designation that will not resolve, send it over — cross-referencing obsolete and foreign grades is routine here.
Common Questions
What buyers and engineers ask most often when a designation does not match the one on the drawing.
It states how the steel was bought, not what is in it. In BS 970 the middle letter says which property the supplier guaranteed: M to mechanical properties, A to chemical analysis, H to hardenability, S for stainless. So 817M40 was supplied against tensile and yield figures, while 535A99 was supplied against a composition analysis. Two bars can share a composition and carry different letters.
No, and the resemblance is a trap. EN19 is a grade - one specific chromium-molybdenum steel. BS EN 10083 is a standard document, a European Norm, covering a whole family of quenched and tempered steels. The two letters are the same by accident: the old British En series and the European EN for Euronorm have nothing to do with each other. A drawing that says EN19 is naming a steel; one that says EN 10083 is naming the specification it must be bought to.
Barely. A Werkstoff number such as 1.7225 is a catalogue reference, not a description. The leading digit gives the material class - 1 for steel, and the cast irons Parkside stocks sit at 0.6025 and 0.7040 - and the following digits place the grade in a group, but nothing in the number tells you the carbon or alloy content. Use the grade equivalents table to turn it into a name that does.
Because both systems put the carbon content last, in hundredths of a percent. AISI 4140 and BS 970's 708M40 are the same steel - roughly 0.40% carbon - and the 40 means the same thing in each. It is the only part of a designation that reads the same across BS 970, AISI and the European names, which makes it the most useful two digits on an unfamiliar drawing.
No - they are near-equivalents, and the designations show it. EN24 is 817M40 in BS 970 and 34CrNiMo6 in the European system. The BS number implies 0.40% carbon; the European name implies 0.34%. Both are correct for their own standard, because the two specifications draw slightly different composition bands around the same steel. For most work they interchange freely; where a specification is tight, check the actual certificate rather than the equivalence.
Work out which system it belongs to first - the shape of the designation tells you. Six characters with a letter in the middle is BS 970. A decimal point after a single digit is a Werkstoff number. Four bare digits is AISI or SAE. A number followed by element symbols is a European name. That narrows the search immediately. If it is still not resolving, call the sales team on 01623 687 660 - cross-referencing obsolete and foreign designations is routine work here.