Fastener Dimensions Reference Guide: Wrench Size, Socket Size & Thread Pitch
Selecting the correct wrench size, drive key size, or thread pitch across different national standards can be a source of costly errors in procurement and assembly. At FULLERKREG, we publish this reference to help engineers, buyers, and maintenance teams quickly cross-reference fastener dimensions across GB, ISO, DIN, ASTM, BSW, and BSF standards.
1. Hex Nut — Across-Flats (S) by Standard (mm)
| Standard | M5 | M6 | M8 | M10 | M12 | M14 | M16 | M18 | M20 | M22 | M24 | M27 | M30 | M33 | M36 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| GB6170 | 8 | 10 | 13 | 16 | 18 | 21 | 24 | 27 | 30 | 34 | 36 | 41 | 46 | 50 | 55 |
| ISO4032 | 8 | 10 | 13 | 16 | 18 | 21 | 24 | 27 | 30 | 32 | 36 | 41 | 46 | 50 | 55 |
| DIN934 | 8 | 10 | 13 | 17 | 19 | 22 | 24 | 27 | 30 | 32 | 36 | 41 | 46 | 50 | 55 |
| GB52 | 8 | 10 | 14 | 17 | 19 | 22 | 24 | 27 | 30 | 32 | 36 | 41 | 46 | 50 | 55 |
Note: GB6170 and GB52 dimensions may differ slightly. Refer to the specific standard for tolerance details.
2. Hex Bolt Head — Across-Flats (S) by Standard
Metric: GB / ISO / DIN (mm)
| Standard | M5 | M6 | M8 | M10 | M12 | M14 | M16 | M18 | M20 | M22 | M24 | M27 | M30 | M33 | M36 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| GB5782/5783 | 8 | 10 | 13 | 16 | 18 | 21 | 24 | 27 | 30 | 34 | 36 | 41 | 46 | 50 | 55 |
| ISO4014/4017 | 8 | 10 | 13 | 16 | 18 | 21 | 24 | 27 | 30 | 32 | 36 | 41 | 46 | 50 | 55 |
| DIN931/933 | 8 | 10 | 13 | 17 | 19 | 22 | 24 | 27 | 30 | 32 | 36 | 41 | 46 | 50 | 55 |
Structural / Imperial Standards (mm)
| Standard | M12 | M14 | M16 | M18 | M20 | M22 | M24 | M27 | M30 | M36 |
|---|---|---|---|---|---|---|---|---|---|---|
| GB1228 | 21 | — | — | — | 34 | — | — | — | — | — |
| AS1252-1996 | — | — | 27 | — | — | 36 | 41 | 46 | 50 | 60 |
| EN14399-3 | 22 | 24 | 27 | 30 | 32 | — | — | — | — | — |
| EN14399-4 | 22 | 24 | — | 30 | 32 | — | — | — | — | — |
ASTM Imperial Sizes — Across Flats (inches)
| Standard | 7/16" | 1/2" | 5/8" | 3/4" | 7/8" | 1" | 1-1/8" | 1-1/4" | 1-3/8" | 1-1/2" |
|---|---|---|---|---|---|---|---|---|---|---|
| A307/A563 | 5/8 | 3/4 | 15/16 | 1-1/8 | 1-5/16 | 1-1/2 | 1-11/16 | 1-7/8 | 2-1/16 | 2-1/4 |
| A325 | 7/8 | — | 1-1/16 | 1-1/4 | 1-7/16 | 1-5/8 | 1-13/16 | 2 | 2-3/16 | 2-3/8 |
3. Socket Head Cap Screw — Drive Key (S) & Head Diameter (dk) (mm)
Per GB70-76, GB70-85, and DIN912.
| Dimension | M3 | M4 | M5 | M6 | M8 | M10 | M12 | M16 | M20 | M24 | M30 | M36 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Drive S (GB70-76) | 2.5 | 3 | 4 | 5 | 6 | 8 | 10 | 14 | 17 | 19 | — | 24 |
| Drive S (GB70-85/DIN912) | 2.5 | 3 | 4 | 5 | 6 | 8 | 10 | 14 | 17 | 19 | 22 | 27 |
| Head dk (GB70-76) | 5.5 | 7 | 8.5 | 10 | 12.5 | 15 | 18 | 24 | 30 | 36 | — | 54 |
| Head dk (GB70-85) | 5.5 | 7 | 8.5 | 10 | 13 | 16 | 18 | 24 | 30 | 36 | 45 | 54 |
Note: DIN912, GB70, ISO4762, and GB70-85 are essentially unified. GB70-76 does not define certain sizes (M14, M18, M22, M27, M33); thread pitch follows GB70-85.
4. Thread Pitch Reference
Metric Coarse & Fine Pitch (mm)
| Diameter | Coarse (mm) | Fine (mm) |
|---|---|---|
| M3 | 0.5 | — |
| M4 | 0.7 | 0.5 |
| M5 | 0.8 | 0.5 |
| M6 | 1.0 | 0.75 |
| M8 | 1.25 | 1 / 0.75 |
| M10 | 1.5 | 1.25 / 1 / 0.75 |
| M12 | 1.75 | 1.5 / 1.25 / 1 |
| M16 | 2 | 1.5 / 1 |
| M20 | 2.5 | 2 / 1.5 / 1 |
| M24 | 3 | 2 / 1.5 / 1 |
| M30 | 3.5 | (3) / 2 / 1.5 / 1 |
| M36 | 4 | 3 / 2 / 1.5 |
Full-thread products use coarse pitch. Fine pitch must be specified explicitly. Values in parentheses are non-preferred.
Unified Imperial Thread (UNC / UNF / UNEF) — TPI
| Size | UNC | UNF | UNEF |
|---|---|---|---|
| 1/4" | 20 | 28 | 32 |
| 5/16" | 18 | 24 | 32 |
| 3/8" | 16 | 24 | 32 |
| 7/16" | 14 | 20 | 28 |
| 1/2" | 13 | 20 | 28 |
| 5/8" | 11 | 18 | 24 |
| 3/4" | 10 | 16 | 20 |
| 7/8" | 9 | 14 | 20 |
| 1" | 8 | 12 | 20 |
| 1-1/4" | 7 | 12 | 18 |
| 1-1/2" | 6 | 12 | 18 |
British Standard Thread (BSW / BSF) — TPI
| Size | BSW | BSF |
|---|---|---|
| 1/4" | 20 | 26 |
| 5/16" | 18 | 22 |
| 3/8" | 16 | 20 |
| 7/16" | 14 | 18 |
| 1/2" | 12 | 16 |
| 5/8" | 11 | 14 |
| 3/4" | 10 | 12 |
| 7/8" | 9 | 11 |
| 1" | 8 | 10 |
| 1-1/4" | 7 | 9 |
| 1-1/2" | 6 | 8 |
Standard Abbreviations Quick Reference
| Code | Full Name | Region |
|---|---|---|
| GB | Guo Biao — Chinese National Standard | China |
| ISO | International Organization for Standardization | International |
| DIN | Deutsches Institut fur Normung | Germany / Europe |
| ASTM | American Society for Testing and Materials | USA |
| UNC | Unified National Coarse | USA / Canada |
| UNF | Unified National Fine | USA / Canada |
| BSW | British Standard Whitworth (coarse) | UK |
| BSF | British Standard Fine | UK |
| TPI | Threads Per Inch | Imperial |
| S | Across-Flats / Wrench Size | All metric |
| dk | Head Diameter (socket screws) | All metric |
Need a Custom or Non-Standard Fastener?
FULLERKREG manufactures standard and non-standard fasteners to DIN, ISO, GB, ASTM, UNI, and ASME specifications across a full range of special alloys. Contact us with your material grade, standard, dimensions, and quantity.
- Material Test Certificates — EN 10204 3.1 / 3.2 on request
- Custom thread forms — metric, unified, Whitworth, ACME, and special profiles
- Global shipping — from our manufacturing base in China worldwide
- Wholesale pricing — OEM and MRO procurement
Contact FULLERKREG — our engineering team will respond promptly.
FULLERKREG — Precision Fasteners. Global Standards. Reliable Supply.