Edition note — October 2026: GB/T 5782-2025 took effect on 1 February 2026 and replaced GB/T 5782-2016. It is a modified adoption of ISO 4014:2022, not an identical adoption. DIN 931-1:1987-09 is withdrawn. Always include the required edition in the enquiry or purchase order. [1] [2] [3]
GB/T 5782, ISO 4014 and DIN 931 are all commonly associated with hexagon head bolts with partial thread.
At first glance, the three standards appear very similar. In many commonly used metric sizes, the bolt geometry, coarse metric thread and general product form are closely aligned.
However, they should not automatically be treated as completely interchangeable standards.
For industrial buyers, fastener manufacturers and engineering teams, the most important differences are found in:
- hex head dimensions,
- standard references,
- mechanical property systems,
- marking and inspection requirements,
- and several specific bolt sizes where the wrench size differs.
Understanding these differences helps avoid incorrect substitutions during quotation, manufacturing and project approval.
1. General Comparison
| Item | GB/T 5782 | ISO 4014 | DIN 931 |
|---|---|---|---|
| Product | Hexagon head bolt | Hexagon head bolt | Hexagon head bolt |
| Thread form | Metric coarse thread | Metric coarse thread | Metric coarse thread |
| Thread coverage | Partial thread | Partial thread | Partial thread |
| Main market | China / GB projects | International market | Legacy DIN / European projects |
| Product grades | Check the specified GB edition | A / B | A / B for DIN 931-1 |
| Standard relationship | 2025 edition modifies ISO 4014:2022 | Current reference: ISO 4014:2022 | Withdrawn DIN 931-1; successor DIN EN ISO 4014 |
| Direct interchangeability | Confirmation recommended | — | Confirmation recommended |
GB/T 5782 and ISO 4014 belong to closely related product families. Compare the specified editions and the actual size before accepting a substitute.
DIN 931 is also very close to ISO 4014, but several important hex head dimensions are different.
2. The Most Important Difference: Hex Head Wrench Size
The dimension that most often causes problems is the width across flats, normally shown as s.
For many bolt sizes, DIN 931 and ISO 4014 use the same width across flats.
However, several common sizes are different.
Key Width Across Flats Comparison
| Nominal Size | DIN 931, s | ISO 4014, s | Difference |
|---|---|---|---|
| M6 | 10 mm | 10 mm | Same |
| M8 | 13 mm | 13 mm | Same |
| M10 | 17 mm | 16 mm | Different |
| M12 | 19 mm | 18 mm | Different |
| M14 | 22 mm | 21 mm | Different |
| M16 | 24 mm | 24 mm | Same |
| M18 | 27 mm | 27 mm | Same |
| M20 | 30 mm | 30 mm | Same |
| M22 | 32 mm | 34 mm | Different |
| M24 | 36 mm | 36 mm | Same |
| M30 | 46 mm | 46 mm | Same |
| M36 | 55 mm | 55 mm | Same |
These are nominal wrench sizes for the listed DIN/ISO series, not complete manufacturing tolerances. The DIN/ISO values are cross-checked against the manufacturer reference in [4]. For a GB/T 5782 order, use the dimensional table in the specified GB edition; do not assume that an ISO value alone demonstrates GB compliance.
This difference is especially important for:
- recessed bolt installations,
- limited wrench clearance,
- socket dimensions,
- maintenance tools,
- existing equipment designed around a DIN bolt head.
For example, a customer specifying DIN 931 M12 may expect a 19 mm width across flats, while an ISO 4014 M12 bolt typically uses 18 mm.
The thread may fit the mating component, but the bolt head may not match the equipment design.
3. Are GB/T 5782 and ISO 4014 the Same?
They are closely related, but the applicable editions matter. The official Chinese standards catalogue records GB/T 5782-2025 as a modified adoption of ISO 4014:2022. The earlier GB/T 5782-2016 was a modified adoption of ISO 4014:2011. [1]
A modified adoption is not a statement that every requirement is identical. Check the specified standard's dimensions, referenced requirements and inspection provisions for the order.
If a purchase order or drawing requires ISO 4014, a GB-only statement of conformity is not sufficient evidence of ISO compliance. Confirm the proposed substitution with the customer and retain the agreed specification in the order documents.
Dimensional compatibility does not automatically mean contractual equivalence.
4. DIN 931 vs ISO 4014
DIN 931 is one of the best-known historical European standards for partially threaded metric hex bolts.
Today, ISO 4014 is generally used as the modern international reference for the same general product category.
For many sizes, DIN 931 and ISO 4014 bolts are dimensionally very similar.
However, the differences in width across flats for M10, M12, M14 and M22 mean that substitution should not be made without checking the drawing or customer specification.
This is particularly important when the bolt head must fit:
- a counterbore,
- a confined installation area,
- a fixed socket,
- or an existing machine design.
5. Thread Length for Partially Threaded Hex Bolts
GB/T 5782, ISO 4014 and DIN 931 all describe partially threaded hex bolts.
The following thread-length relationship is commonly used for ISO 4014 / legacy DIN 931 reference dimensions, subject to the permitted diameter and length combinations. It is a selection aid, not a universal rule for every bolt length. [5]
| Bolt Length L | Typical Thread Length b |
|---|---|
| L ≤ 125 mm | b = 2d + 6 |
| 125 < L ≤ 200 mm | b = 2d + 12 |
| L > 200 mm | b = 2d + 25 |
Where:
- d = nominal bolt diameter, in mm
- L = nominal bolt length measured from beneath the head, in mm
- b = reference thread length, in mm
For example, for an M16 × 100 bolt:
b = 2 × 16 + 6 = 38 mm
For production, use the specified edition's dimensional table, permitted length combinations, thread run-out and shank requirements. Do not apply the formula where it would leave no compliant plain shank, and do not treat L − b as a guaranteed minimum unthreaded length.
6. Do Not Confuse Partially Threaded and Fully Threaded Standards
This is a common quotation and production mistake.
The corresponding product families are:
| Partially Threaded Hex Bolt | Fully Threaded Hex Bolt |
|---|---|
| GB/T 5782 | GB/T 5783 |
| ISO 4014 | ISO 4017 |
| DIN 931 | DIN 933 |
Therefore:
ISO 4014 is not the same product as ISO 4017.
Similarly:
DIN 931 is not the same product as DIN 933.
The difference is primarily the threaded length of the bolt shank.
7. Product Standard vs Mechanical Property Standard
ISO 4014, GB/T 5782 and DIN 931 are product standards, covering dimensions and associated technical requirements. They are not stand-alone material specifications.
They do not by themselves fully define the material or strength class.
For example:
ISO 4014 M16 × 100 A4-80
should be interpreted as:
- Product standard: ISO 4014
- Nominal size: M16
- Length: 100 mm
- Stainless steel grade designation: A4
- Property class: 80
ISO 4014 refers to ISO 3506-1 for stainless steel fastener grades and property classes, and ISO 898-1 for carbon and alloy steel fastener property classes. The required material, property class and applicable edition must still be specified. [2]
For carbon and alloy steel bolts, property classes such as:
- 8.8
- 10.9
- 12.9
are controlled by the applicable mechanical property standard rather than by ISO 4014 itself.
This distinction is important when preparing quotations and material certificates.
8. Can GB/T 5782 Replace ISO 4014?
A GB/T 5782 bolt may be a suitable dimensional match, but the proposed product must be checked against the specified ISO edition and the actual order requirements.
However, if the customer's purchase order specifies:
ISO 4014
the safest approach is to supply and certify the product to ISO 4014 unless the customer approves an equivalent GB/T standard.
For international projects, the requested standard should remain the governing standard on:
- quotation,
- purchase order,
- production documentation,
- inspection records,
- certificate of conformity.
9. Can DIN 931 Replace ISO 4014?
In many common sizes, the dimensions are very close.
However, substitution requires special attention to:
M10, M12, M14 and M22
because the width across flats differs.
A bolt may still thread correctly into the mating nut or tapped hole, but the head dimensions can affect installation and tool compatibility.
Therefore, DIN 931 and ISO 4014 should be treated as:
closely related standards, not automatically interchangeable products.
10. Quick Sales Reference
| Customer Requirement | Recommended Interpretation | Direct Substitution? |
|---|---|---|
| GB/T 5782 | Chinese partially threaded hex bolt standard | — |
| ISO 4014 | International partially threaded hex bolt standard | — |
| DIN 931 | Legacy DIN partially threaded hex bolt standard | — |
| GB/T 5782 → ISO 4014 | Usually dimensionally close | Customer approval recommended |
| DIN 931 → ISO 4014 | Usually close | Check M10/M12/M14/M22 carefully |
| DIN 931 → GB/T 5782 | Usually close | Check head dimensions before substitution |
11. What Should Be Confirmed Before Quotation?
When a customer only sends a requirement such as:
M16 × 80 Hex Bolt
that information is not sufficient for a reliable quotation.
At minimum, confirm:
- Product standard: ISO 4014, DIN 931 or GB/T 5782
- Material: carbon steel, alloy steel or stainless steel
- Property class: 8.8, 10.9, A2-70, A4-80, etc.
- Thread requirement: coarse or fine thread; ISO 4014 covers coarse pitch, so a fine-pitch requirement needs the appropriate product standard
- Surface finish: plain, zinc plated, hot dip galvanized, PTFE, etc.
- Inspection and documentation: specify whether a COC, MTC, EN 10204 3.1 inspection certificate, PMI or other project inspection is required, and agree the document scope
Key Takeaway
GB/T 5782, ISO 4014 and DIN 931 all cover the same general fastener category: metric partially threaded hexagon head bolts.
Their dimensions are highly similar, but they should not automatically be treated as completely interchangeable.
The most important practical differences are:
Check the GB/ISO edition and adoption relationship, and pay particular attention to the DIN/ISO head widths for M10, M12, M14 and M22.
For engineering projects, the standard specified in the drawing or purchase order should always remain the primary manufacturing and inspection basis.
Frequently Asked Questions
Is DIN 931 equivalent to ISO 4014?
DIN 931 and ISO 4014 cover very similar partially threaded hex bolts, but they are not completely identical. Certain sizes, especially M10, M12, M14 and M22, have different widths across flats.
Is GB/T 5782 equivalent to ISO 4014?
GB/T 5782-2025 is a modified adoption of ISO 4014:2022. That relationship does not establish identical requirements or automatic interchangeability. Check the specified editions, size and agreed documentation.
What is the difference between ISO 4014 and ISO 4017?
ISO 4014 covers partially threaded hexagon head bolts, while ISO 4017 covers fully threaded hexagon head screws/bolts.
Can DIN 931 bolts be used instead of ISO 4014 bolts?
Sometimes, but substitution should be checked against the drawing and application. Head dimensions may differ even when the thread size is the same.
Need Help Confirming a Hex Bolt Specification?
WISINE supports industrial fastener projects with material selection, dimensional review, thread confirmation and quotation preparation for stainless steel, duplex stainless steel, nickel alloy and alloy steel fasteners.
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References and Edition Notes
- SAMR — GB/T 5782-2025: current status, implementation date and modified adoption of ISO 4014:2022
- ISO — ISO 4014:2022: scope and property-standard references
- DIN Media — DIN 931-1:1987-09: withdrawn status and successor documents
- Würth — Differences between DIN, EN and ISO standards, Table 7, page 11
- Dueemme Sidol — ISO 4014 reference dimensions and thread-length limitations
- ISO — ISO 4017:2022: hexagon head screws
This article supports specification review. Reference dimensions and comparisons do not replace the complete standard, the approved drawing or the order-specific inspection requirements.
