Walk into any fastener stockist and you’ll see DIN numbers everywhere. But what does DIN actually mean, and how does it relate to ISO and ASME standards? This plain-English guide explains the main systems and how to use them.
- DIN = Deutsches Institut für Normung — the German national standards body.
- Most DIN fastener standards have been superseded by ISO equivalents (e.g. DIN 934 → ISO 4032).
- DIN numbers remain in common everyday use — PTS stocks to both.
- ASME B18.2.2 covers American inch fasteners (UNC/UNF thread).
- PTS covers DIN/ISO metric and ASME inch standards across all categories.
What is DIN?
DIN stands for Deutsches Institut für Normung — the German standards body. From the mid-20th century, DIN published the most widely adopted set of fastener standards in Europe, covering geometry, dimensions, tolerances and materials.
You still see DIN numbers everywhere because an entire generation of engineers, designers and buyers learned to specify by DIN. The numbers are memorable, well-documented and supported by decades of cross-references in design software and catalogues.
How ISO relates to DIN
From the 1980s onwards, the International Organisation for Standardisation (ISO) systematically replaced many DIN fastener standards with international equivalents. The dimensions are usually identical or near-identical — the standard number just changed.
| Old DIN number | New ISO standard | Product |
|---|---|---|
| DIN 931 | ISO 4014 | Hexagon head bolt (part-threaded) |
| DIN 933 | ISO 4017 | Hexagon head screw (full-threaded) |
| DIN 934 | ISO 4032 | Hexagon full nut |
| DIN 912 | ISO 4762 | Socket cap screw |
| DIN 125 | ISO 7089 | Plain washer (flat) |
| DIN 127 | ISO 7090 | Spring washer |
In practice, a part supplied to DIN 934 will be dimensionally interchangeable with ISO 4032. PTS stocks to both references, and our product listings carry both numbers where applicable.
ASME and inch fasteners
ASME B18.2.2 (American Society of Mechanical Engineers) covers inch-series fasteners with UNC (Unified National Coarse) and UNF (Unified National Fine) threads — the standard for North American engineering and the dominant system in industries with US heritage such as aerospace and oil & gas.
PTS holds one of the largest stocks of stainless ASME inch fasteners outside the USA — covering the full UNC and UNF range in A2 and A4 stainless, with the same certification and traceability as our metric lines.
Frequently asked questions
Are DIN and ISO fasteners interchangeable?
Why do PTS product listings still show DIN numbers?
Can I mix metric and imperial (UNC/UNF) fasteners?
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