What is the difference between DIN 931 and ISO 4014?

DIN 931 and ISO 4014 are both partially threaded hex bolt standards. ISO 4014 is the international harmonisation of DIN 931, with minor dimensional adjustments to thread length calculations and head tolerances. For most practical applications, they are interchangeable.

Are DIN and ISO bolt dimensions interchangeable?

In most cases, yes. ISO standards were developed to harmonise European DIN standards with international requirements. Dimensional differences are typically within tolerance ranges. However, for critical applications, always verify against the specific standard required by your project specification.

What is the difference between heavy hex and standard hex nuts?

Heavy hex nuts have larger across-flats dimensions and greater height than standard hex nuts. This provides increased bearing surface and thread engagement, making them suitable for high-strength structural and pressure applications where ASTM A194 and ASME B18.2.2 specifications apply.

How are stud bolt lengths measured?

Stud bolt length is measured as the overall length from end to end, including both threaded portions and the unthreaded shank. This differs from hex bolt measurement which is measured from under the head. For double-end studs, specify the total length plus thread lengths at each end.

TECHNICAL REFERENCE

Dimensional Standardsfor Industrial Fasteners

EMG supplies fasteners manufactured to recognised international dimensional standards including DIN, ISO, EN and ASTM specifications. This page serves as a technical reference for commonly supplied fasteners.

STANDARDSDIN • ISO • EN • ASTM

Hex Bolts Stud Bolts Nuts Washers Structural Threads

METRIC STANDARDS

Hex Bolts – Metric Standards

Hexagon head bolts are the most widely used fastener type in industrial applications. Metric hex bolts are manufactured to DIN and ISO standards, with ISO specifications representing the international harmonisation of European DIN standards.

DIN 931

Partially Threaded Hex Bolts

Hexagon head bolts with a partial thread, leaving an unthreaded shank beneath the head. Suitable for applications requiring shear resistance in the unthreaded portion.

Thread calculated based on diameter + length

Structural and mechanical assemblies

DIN 933

Fully Threaded Hex Bolts

Hexagon head bolts with thread extending to the head. Ideal for applications requiring maximum thread engagement or where the bolt passes through thin materials.

Full length minus transition zone

Thin material applications

ISO 4014

Hex Bolts (Partial Thread)

International equivalent of DIN 931 for partially threaded hex bolts. Minor dimensional adjustments exist but for most applications the standards are interchangeable.

Product grades A and B available

Harmonised with DIN 931

ISO 4017

Hex Bolts (Full Thread)

Corresponds to DIN 933 for fully threaded hexagon bolts. Product grade A (precision) and grade B (standard) dimensional tolerances available.

Property classes per ISO 898-1

Harmonised with DIN 933

Key Dimensional Characteristics

HEADAcross flats (s) and head height (k)

THREADb = 2d + 6mm (partial thread)

TOLERANCEProduct grade A (6g) or B

PROPERTY8.8, 10.9, 12.9 per ISO 898-1

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THREADED FASTENERS

Stud Bolts & Threaded Rod Standards

Stud bolts and threaded rod are manufactured to DIN, ASME and project-specific specifications. Length measurement conventions and thread engagement requirements vary by standard and application.

DIN 975

Fully Threaded Rod

Metric threaded rod with continuous thread along the entire length. Standard lengths 1000mm and 2000mm.

ISO metric coarse pitch

Cut-to-length stud production

DIN 976

Stud Bolts

Double-end stud bolts with defined thread lengths at each end separated by an unthreaded shank.

Type A: equal threads

Type B: tap end engagement

ASME B18.31.2

Continuous Thread Studs

Inch-series continuous thread studs for pressure equipment. UNC and 8UN thread series.

Thread class 2A standard

Class 3A for precision

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NUT SPECIFICATIONS

Nut Dimensional Standards

Hex nuts are manufactured to DIN, ISO and ASME standards. Dimensional differences between standard and heavy hex configurations affect bearing surface area, thread engagement depth, and compatibility with bolting assemblies.

DIN 934

Hex Nuts

Legacy standard

Standard hexagon nuts with metric coarse thread. Superseded by ISO 4032 for new designs but still widely referenced.

ISO 4032

Style 1 Hex Nuts

Standard height

Hexagon nuts with height approximately 0.8d. Suitable for property class up to 10 when paired with equivalent bolts.

ISO 4033

Style 2 Hex Nuts

Increased height

Hexagon nuts with increased height (approximately 0.9d) providing greater thread engagement for high-strength assemblies.

ASME B18.2.2

Heavy Hex Nuts

Larger bearing area

Heavy hex nuts for inch-series fasteners. Larger across-flats than standard hex, essential for ASTM A194 pressure applications.

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WASHER SPECIFICATIONS

Washer Dimensional Standards

Flat washers distribute load, protect surfaces, and span oversized holes. Dimensional standards define inside diameter, outside diameter, and thickness for general-purpose and structural applications.

General Purpose Washers

DIN 125

Flat washers for general engineering. Form A (no chamfer), Form B (chamfered).

DIN 9021

Large OD washers (≈3× bolt diameter) for soft materials and timber.

ISO 7089 / 7090

International equivalent of DIN 125. Hardness grades 200 HV and 300 HV.

Dimensional Elements

d₁

Inside Diameter
Bolt clearance hole

d₂

Outside Diameter
Bearing surface extent

Thickness
Load distribution

Hardness
200 or 300 HV

STRUCTURAL BOLTING

EN Structural Bolting Systems

European structural bolting standards define complete fastener systems for steel construction. The EN 14399 series covers preloaded assemblies, while EN 15048 addresses non-preloaded applications.

EN 14399

High-Strength Structural Bolting

Multi-part standard covering preloaded structural bolting assemblies. Matched bolt, nut, and washer sets for controlled preload in friction-grip and slip-critical connections.

HV System

Controlled hardness bolt/nut

HR System

Reduced hardness nut

EN 15048

Non-Preloaded Structural Bolting

Structural bolting assemblies for non-preloaded applications. Bearing-type connections where bolts are tightened to snug-tight condition.

Applications: Secondary steelwork, static loading, bearing-type connections

THREAD SPECIFICATIONS

Thread Forms & Tolerance Classes

Thread form and tolerance class determine fit, interchangeability, and assembly characteristics. Metric and unified inch thread systems each have defined tolerance designations.

Metric Thread Series

Coarse pitche.g., M12 × 1.75

Fine pitche.g., M12 × 1.25

6g toleranceExternal thread

6H toleranceInternal thread

Unified Inch Thread Series

UNCe.g., 1/2-13 UNC

UNFe.g., 1/2-20 UNF

Class 2A/2BStandard fit

Class 3A/3BClose fit

COMMON QUESTIONS

Frequently Asked Questions

Require fasteners to these dimensional standards?

Our technical team can advise on specification and supply fasteners to DIN, ISO, EN and ASTM requirements with full EN 10204 3.1 certification.

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