How to Read EN Aerospace Part Numbers: A Practical Guide

EN6115-4-08. EN2408. If you buy hardware for European aircraft programs, part numbers that begin with EN cross your desk constantly, and every character in them is doing a job. An EN aerospace callout is not a random SKU: it is a compressed description of a standard, a size, a material, and a set of optional features, written in the European aerospace convention rather than the US one. Learn to unpack it and you can sanity-check a quote in seconds, catch a transcription error before it becomes a wrong shipment, and ask suppliers sharper questions.

This guide walks through the anatomy of EN aerospace part numbers the way a distributor reads them at the quoting desk and on the receiving dock, with particular attention to metric bolts and to bearings, two families that come up over and over. It stays honest about the limits, too: dash-number semantics vary from one standard to the next, and the EN or ASD-STAN standard sheet, not a blog post, is always the final authority.

Where EN Aerospace Numbers Come From

EN aerospace standards are European Norm (EN) standards for the aerospace series. They are developed by ASD-STAN, the standardization body of the AeroSpace and Defence Industries Association of Europe, and published as EN documents under CEN, the European Committee for Standardization. In practice you will see them all over Airbus and other European airframe and engine programs, sitting alongside manufacturer-specific systems such as the Airbus ABS series and the older NSA numbers.

The defining characteristic for a buyer coming from a US background is that EN aerospace parts follow European aerospace standards, not the American NAS, AN, or MS families, and many of them are metric. An EN bolt and a dimensionally similar NAS bolt are not the same part, and they are not interchangeable without engineering authority. That single fact prevents a large share of the mistakes in a mixed bill of materials.

The Anatomy of an EN Part Number

Most EN aerospace callouts have up to three layers:

1. The prefix, EN, identifying the European Norm aerospace series.
2. The base number (for example 6115, 2408), which identifies the standard itself, and with it the part family: type, head or body style, general material system, and every fixed characteristic.
3. Dash numbers and letter codes, which select the variable characteristics: diameter, length, material option, finish, locking features, and so on, frequently in millimetres.

As with the US systems, the boundary between layers moves from one family to the next. In some standards the base number is purely an identifier and every dimension lives in the dash numbers; in others part of the size is folded into the base. There is no single universal parsing rule for EN aerospace numbers: you learn the families you buy most, and you look up the rest against the current standard sheet.

Metric Versus Inch: The Distinction That Matters

The most important habit when reading EN callouts is to remember that you are usually in millimetres, not sixteenths of an inch. Where a NAS bolt dash number often expresses grip in inch fractions, EN aerospace dimensions are commonly metric, and a dash number that looks familiar can mean something completely different.

This matters most at the interface between systems. If a drawing mixes EN parts with NAS or MS parts, do not assume a shared unit convention across the callouts, and do not mentally convert one standard's dash number into another's. Read each callout on its own standard's terms. Thread forms are part of the same trap: metric threads and Unified inch threads are not interchangeable even when nominal diameters look close, so an EN metric bolt does not drop into a hole tapped for an inch-series fastener.

Families a Buyer Sees Most

The EN aerospace series is broad, but a handful of families make up the bulk of day-to-day procurement:

• Fasteners: bolts, screws, nuts, and washers, covering a wide range of metric threaded hardware. You can browse these in our bolts and washers catalogs.
• Bearings: rod-end and spherical bearings, a large and frequently searched EN family that we treat in detail in the next section.
• Rivets and other installed hardware: solid and blind rivets and related fastening elements defined under EN aerospace standards.

The safest way to move from a callout to a real part is to search the full EN number against a catalog rather than reconstructing it from a description. You can search the entire range in our parts catalog.

EN Bearings: A Family Worth Learning

EN aerospace bearings deserve their own attention. Rod-end bearings and spherical (self-aligning) bearings show up throughout control linkages, actuation, and structural pivots, and they are one of the most searched EN categories we see. They are also easy to mis-order, because the callout has to pin down a bore or shank size, a housing or head configuration, a material system, and often a self-lubricating liner option, all in a compact string.

When you read an EN bearing callout, work through the same three layers, but expect the dash numbers and letters to carry more of the meaning than they do for a plain bolt:

• The base number fixes the bearing type: for instance, a rod-end style versus a plain spherical bearing, and the broad construction the standard covers.
• The dash numbers typically index the size, often tied to a bore or shank dimension in millimetres, but the exact mapping is standard-specific and must be read from the sheet.
• Letter codes commonly select the material or the liner and lubrication option, distinguishing, for example, a self-lubricating lined bearing from a metal-on-metal one.

Because the liner and material options change the load rating and the qualification of the bearing, never treat those letters as optional detail. Two EN bearing callouts that differ by a single letter can be genuinely different parts. You can browse the range in our aerospace bearings catalog and confirm the exact configuration against the standard before you commit an order.

Worked Examples: An EN Bolt and an EN Bearing

Take a bolt-style callout of the form EN6115-4-08 and read it layer by layer:

1. EN: the part is defined by a European Norm aerospace standard, developed through ASD-STAN and published under CEN.
2. 6115: the base number places it in a specific EN fastener standard, fixing the head style, thread form, and base material system for the whole family.
3. -4: a size index. In a metric fastener family a dash like this typically points to a nominal diameter, but the precise value comes from the standard's size table rather than from arithmetic, so confirm it.
4. -08: a length index, again usually metric. Whether it reads directly as millimetres or as a table position depends on the standard, so verify before ordering.

Now a bearing-style callout such as EN2408. Here the base number identifies the bearing standard and its construction, and any trailing dash numbers and letters would select the size and the liner or material option. The reading discipline is the same: the base tells you what kind of bearing it is, the suffixes tell you which member of the family, and the standard sheet is what turns those suffixes into real millimetre dimensions and load ratings. Do not assert an exact bore or length from the number alone.

Reverse the exercise as a check. If a requisition adds or drops a trailing letter on either example, treat it as a change to the part, not as noise, and resolve exactly what it means before quoting.

Common Pitfalls

• Metric versus inch confusion. The single most common EN error is reading a dash number as inch fractions out of NAS habit. EN aerospace dimensions are frequently metric; parse them in millimetres and never carry a US convention across into an EN callout.
• Family-specific dash semantics. A -4 that means diameter in one EN family can mean length, or a table position, in another. Parse each standard on its own terms rather than assuming the pattern transfers.
• Dropped characters. A missing letter or a transposed digit produces a real, orderable, and wrong part number more often than you would hope, and on bearings it can quietly swap the liner or material option. Copy callouts character-for-character and have receiving verify markings against the purchase order, not against memory.
• Superseded EN and ASD-STAN standards. EN and ASD-STAN standards are revised, replaced, and withdrawn over time. If a drawing calls an older standard, buy exactly what your engineering authority requires and check the standard's current status rather than silently substituting a successor.
• EN-versus-NAS/MS lookalikes. An EN metric bolt and a NAS or MS inch bolt can look interchangeable in a description and even in nominal size, but they differ in units, thread form, material, and qualification. They are not interchangeable unless the engineering authority for your application says so in writing.

If you also work with the US and manufacturer systems, our companion guides cover reading NAS part numbers, Airbus ABS part numbers, and NSA part numbers, so you can move confidently between the conventions on a mixed bill of materials.