Fastener Standards
Find and compare common DIN, ISO and EN standards for screws, bolts, nuts, washers and other industrial fasteners.
Fastener standards define important characteristics such as dimensions, thread type, head shape, drive type, tolerances and mechanical properties. Choosing the correct standard helps ensure that a fastener fits properly, performs as expected and is compatible with the other components in an assembly.
This POLT24 reference guide provides a practical starting point for understanding commonly used fastener standards and finding suitable products in our catalogue.
Knowledge base under continuous development: we are gradually adding detailed standard pages, dimensional information, technical drawings, material guidance and links to matching products.
What are DIN, ISO and EN fastener standards?
Industrial fasteners are commonly specified using standards published by organisations such as DIN, ISO and CEN:
- DIN standards originate from the German Institute for Standardization and remain widely used throughout European engineering and trade.
- ISO standards are international standards intended to provide consistent specifications across countries and industries.
- EN standards are European standards adopted by the national standards organisations of participating European countries.
Many older DIN fastener standards have corresponding ISO or EN standards. However, a corresponding standard should not automatically be treated as completely identical. Dimensions, tolerances, width across flats, head geometry, material requirements or available size ranges may differ between editions.
Popular screw and bolt standards
| Standard | Fastener type | Related standard | Typical application |
|---|---|---|---|
| DIN 912 | Hexagon socket head cap screw | ISO 4762 | Machinery, equipment, tooling and compact assemblies |
| ISO 7380-1 | Hexagon socket button head screw | Commonly associated with DIN 7380 | Assemblies requiring a low-profile, rounded head |
| DIN 7991 | Hexagon socket countersunk head screw | ISO 10642 | Flush-mounted assemblies and countersunk holes |
| DIN 931 | Hexagon head bolt with partial thread | ISO 4014 | Structural, mechanical and general-purpose assemblies |
| DIN 933 | Hexagon head screw with full thread | ISO 4017 | General construction, machinery and maintenance |
| DIN 603 | Carriage bolt with square neck | ISO 8677 | Timber, furniture and assemblies requiring anti-rotation |
Popular nut standards
| Standard | Fastener type | Related standard | Typical application |
|---|---|---|---|
| DIN 934 | Hexagon nut | ISO 4032 | General-purpose bolted joints |
| DIN 985 | Prevailing-torque hexagon nut with non-metallic insert | ISO 10511 | Assemblies exposed to vibration or movement |
| DIN 439 | Thin hexagon nut | ISO 4035 | Locking, adjustment and space-limited assemblies |
| DIN 557 | Square nut | — | Channels, furniture, machinery and captive-nut applications |
| DIN 1587 | Hexagon domed cap nut | — | Protecting exposed threads and improving appearance |
Popular washer standards
| Standard | Fastener type | Related standard | Typical application |
|---|---|---|---|
| DIN 125 | Flat washer | ISO 7089 / ISO 7090 | General load distribution under screws, bolts and nuts |
| DIN 9021 | Large outside-diameter flat washer | ISO 7093-1 | Soft materials, sheet metal and larger bearing surfaces |
| DIN 127 | Split spring lock washer | — | Traditional locking applications |
| DIN 6796 | Conical spring washer | — | Highly preloaded bolted joints |
How to choose the correct fastener standard
A standard number alone does not describe every property of a fastener. Before ordering, check the complete product specification, including:
- Fastener type: screw, bolt, nut, washer, pin or threaded insert
- Thread diameter: for example M3, M6 or M12
- Thread pitch: coarse or fine metric thread
- Length: measured according to the head style and applicable standard
- Material: carbon steel, stainless steel, brass or another alloy
- Property class: for example 8.8, 10.9 or 12.9
- Stainless-steel grade: for example A2 or A4
- Surface finish: plain, zinc plated, black oxidised or another coating
- Head and drive type: hexagon, internal hexagon, Torx, Phillips or Pozidriv
Are DIN and ISO standards interchangeable?
Some DIN standards have been withdrawn or superseded by ISO or EN standards, and products made to the newer standard may be suitable replacements in many applications. Nevertheless, the standards are not always dimensionally identical.
For example, a related DIN and ISO fastener may differ in head height, head diameter, width across flats, thread range, tolerances or mechanical requirements. For critical, safety-related or tightly dimensioned assemblies, always compare the applicable standard documents, technical drawings and product specifications before substitution.
Fastener materials and strength classes
The same dimensional standard may be available in several materials and strength classes. The correct choice depends on load, environment, temperature, corrosion exposure and assembly requirements.
Carbon and alloy steel
Steel fasteners are commonly supplied in property classes such as 8.8, 10.9 and 12.9. A higher property class generally indicates greater tensile and yield strength, but it does not automatically make the fastener suitable for every application.
Stainless steel
A2 stainless steel is widely used for general corrosion resistance in indoor and moderately exposed environments. A4 stainless steel provides improved resistance in more demanding environments, including many marine, chemical and outdoor applications.
Surface coatings
Zinc plating and other coatings can improve corrosion resistance, alter appearance or support specific assembly requirements. Coating thickness can also affect thread fit and should be considered in precision applications.
Frequently asked questions
What does DIN mean on a screw or bolt?
DIN indicates that the fastener is manufactured according to a standard published by the German Institute for Standardization. The standard usually defines its geometry, dimensions, tolerances and other technical characteristics.
What does ISO mean for fasteners?
ISO fastener standards provide internationally recognised specifications intended to improve compatibility and consistency between manufacturers and markets.
Does the standard define the material?
Not always. A dimensional standard primarily describes the shape and dimensions of the fastener. Material, strength class, stainless-steel grade and coating may be defined by separate standards or by the complete product specification.
Can I replace a DIN fastener with its ISO equivalent?
Often, but not automatically. Always verify dimensions, mechanical properties, thread specifications and application requirements before replacing one standard with another.
How is screw length measured?
Most screw lengths are measured from beneath the head to the end of the screw. Countersunk screws are normally measured over their full length, including the head. The applicable dimensional standard should always be checked when accuracy is important.
Explore fasteners by category
Browse the POLT24 catalogue to find fasteners by type, size, material and standard:
Please verify the category URLs before publication and replace them if your final PrestaShop category addresses differ.
POLT24 fastener knowledge base
We are expanding this section into a detailed technical resource covering individual DIN, ISO and EN standards, dimensional tables, standard comparisons, thread information, materials, strength classes and practical selection guides.
Planned additions include:
- Individual pages for commonly used DIN and ISO standards
- Fastener dimensions and technical drawings
- DIN-to-ISO comparison guides
- Metric thread diameter and pitch tables
- Steel property-class guidance
- A2 and A4 stainless-steel comparisons
- Compatible nuts, washers and related products
- Direct links to in-stock POLT24 fasteners
Important: this guide is provided as general product-selection information. For engineering, structural, safety-critical or regulated applications, consult the official standard, project documentation and a qualified engineer.
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