Engineering Guide · 6 min read
DIN 934 vs ISO 4032: Hex Nut Dimensions and Differences
Compare DIN 934 and ISO 4032 hex nuts: wrench sizes, nut height, coarse and fine threads, strength requirements and what to check before substitution.
The short answer: DIN 934 and ISO 4032 hex nuts can share the same metric thread while differing in wrench size and height. Before substituting one for the other, compare those dimensions, the thread pitch and the specified mechanical properties. DIN 934:1987-10 is withdrawn; ISO 4032:2023 covers coarse-pitch regular hex nuts, while ISO 8673:2023 covers the fine-pitch form.[1][2][3][4]
This article is part of How to Specify a Bolt. It explains what to check when a drawing, purchase order or supplier quotation names DIN 934. For inch hex nuts, use the separate ASME hex nut dimension tables.
What DIN 934 and ISO 4032 specify
DIN 934 identifies a conventional external hexagon nut with a metric internal thread. Its 1987 edition covers both coarse and fine pitches, with product grades A and B. DIN Media lists the edition as withdrawn, with replacements that include the European adoptions of ISO 4032 and ISO 8673.[1]
For a new specification, choose the product standard that matches the thread:
| Requirement | Standard | Scope to check |
|---|---|---|
| Existing DIN drawing | DIN 934:1987-10 | Legacy coarse- or fine-pitch hex nut. Keep the drawing requirement until a replacement is approved. |
| Coarse-pitch regular nut | ISO 4032:2023 | Style 1 steel and stainless steel nuts; main scope M5–M39, product grades A and B.[2] |
| Fine-pitch regular nut | ISO 8673:2023 | Style 1 steel and stainless steel nuts; main scope 8–39 mm thread diameter, product grades A and B.[3] |
The edition matters at the ends of the size range. ISO 4032:2023 moves historical sizes below M5 and above M39 into informative Annex A. When ordering those sizes, agree the dimensions and mechanical requirements explicitly rather than extending an M5–M39 table.[2]
Compare wrench size and nut height
A nut that threads onto the bolt may still change the assembly. The nominal thread diameter D, width across flats s and nut height m describe three different features. Check the tool envelope and bolt projection as well as the thread.
The four wrench-size changes are shown below. Values are in millimeters and compare the legacy DIN series with the ISO series in Würth’s technical comparison; the ISO values also match Tables 1 and 2 of ISO 4032:2023.[4][2]
| Nominal thread | DIN 934 across flats, s | ISO 4032 across flats, s |
|---|---|---|
| M10 | 17 mm | 16 mm |
| M12 | 19 mm | 18 mm |
| M14 | 22 mm | 21 mm |
| M22 | 32 mm | 34 mm |
These are nominal wrench sizes, corresponding to the maximum across-flats dimension in the ISO tables. Minimum across flats, width across corners, bearing-face dimensions and chamfers require their own checks. A socket’s outside diameter also needs clearance around the nut.
Height changes can matter even where the wrench size stays the same. For example, Würth’s comparison gives an M12 maximum nut height of 10 mm for DIN 934 and 10.8 mm for ISO 4032; ISO 4032:2023 Table 1 confirms the 10.8 mm maximum. These are dimensional limits, not measurements of supplied parts. Check the available threaded length, engagement and clearance above the nut against the proposed part’s full drawing.[4][2]
Check pitch before choosing the ISO standard
ISO 4032 is the coarse-pitch route. For a regular hex nut with metric fine-pitch thread, check ISO 8673:2023 and state the pitch on the order.[2][3] A quotation that reads only “DIN 934 / ISO 4032” leaves the fine-pitch requirement unresolved.
For example, M12 × 1.75 specifies a 12 mm nominal thread diameter and a 1.75 mm pitch; that is the M12 coarse pitch in ISO 4032:2023. The 18 mm wrench size is a separate dimension.[2] Use Metric and Inch Callouts to read the size string. When replacing unmarked hardware, record the mating bolt’s diameter and pitch using the thread pitch gauge procedure, then confirm the nut specification with the supplier.
Specify nut strength separately
Product grades A and B concern dimensional accuracy. Mechanical property classes and material grades are separate requirements: ISO 898-2:2022 covers carbon and alloy steel nuts with specified property classes; ISO 3506-2:2020 covers stainless steel nuts with specified grades and property classes.[5][6]
For legacy DIN 934 stock, request the mechanical standard behind the class marking and the proof-load documentation before comparing it with an ISO nut. Würth’s comparison distinguishes older DIN 267-4 load requirements from the ISO nut requirements.[4]
For a steel nut, ask for its nut property class and proof-load requirements. A bolt designation such as 8.8 or 10.9 on a combined hardware listing leaves the nut class to be confirmed. Record the bolt and nut requirements separately, then verify their pairing for the connection. See Fastener Grades Explained for the different designation systems.
For stainless steel, specify both the steel grade and the nut property class. “A2” or “A4” alone leaves the strength requirement incomplete; the stainless fastener marking guide explains the distinction. For an ASTM bolting assembly, follow its specified nut grade and the ASTM A194 nut requirements rather than selecting by hex shape.
When can ISO 4032 replace DIN 934?
Accept the substitution once the proposed nut meets the connection’s requirements and the drawing owner approves the change. Review these items together:
- Thread: nominal diameter, pitch, thread tolerance and fit with the finished mating bolt.
- Space: across flats and corners, socket clearance, nut height, bearing surface and available bolt projection.
- Load and finish: nut material, property class, proof-load requirements and the specified coating or surface condition.
- Documents: the proposed standard and edition, supplier drawing, inspection documents and written approval of any departure from the original order.
Keep the specified finish in that comparison. For a coated assembly, confirm the thread fit and the installation procedure for the actual bolt, nut and coating combination. The bolt torque guide explains which joint conditions must accompany a tightening value.
What to put on the RFQ
A new coarse-pitch steel nut inquiry can start with this example:
Hexagon regular nut (style 1) — ISO 4032:2023 — M12 × 1.75 — steel, property class 8 to ISO 898-2:2022 — plain (uncoated) — 1,000 pieces
Complete it with the mating bolt specification, any controlled clearances, required inspection documents and delivery requirements. This example describes an uncoated nut; specify the actual finish needed for the application.
For an existing drawing, quote DIN 934:1987-10 with its required thread, material, mechanical properties and finish. Ask the supplier to identify any proposed ISO replacement and list dimensional or mechanical differences for approval. That keeps a stock substitution visible before the parts reach assembly.
References
- DIN Media. DIN 934:1987-10. Official scope, withdrawn status and replacement record for coarse- and fine-pitch hexagon nuts.
- ISO. ISO 4032:2023 — Fasteners — Hexagon regular nuts (style 1). Scope and foreword; Clause 4 and Tables 1–2 for dimensions.
- ISO. ISO 8673:2023 — Hexagon regular nuts (style 1), with fine pitch thread. Public scope and current edition.
- Würth Industrie Service. CONNECT Band I — Normung, Sections 23 and 25, printed pages 16 and 18–19. Supplier’s historical DIN-to-ISO comparison. Selected wrench sizes and M12 maximum heights are used here; its older mechanical-standard references are not current specifications.
- ISO. ISO 898-2:2022. Mechanical and physical properties of carbon and alloy steel nuts, including property classes and proof load.
- ISO. ISO 3506-2:2020. Mechanical and physical properties of stainless steel nuts with specified grades and property classes.
For a quotation, send the drawing and nut specification, including the thread, material, finish and any proposed substitution.