Do you ever struggle to remember the relationship between a metric hex bolt thread size and the related hex head size (between the flats, or ‘wrench’ size).
Or, do you have a design with limited clearance? Use this table to see if you have room, but don’t forget to check that you have enough room for a socket or a wrench to get in there. Otherwise, you might be better off using a Socket Head Cap Screw (SHCS) instead of a Hex Head fastener.
The first column (ANSI/ISO) is pertinent to ‘standard’ metric hex bolts:
| Bolt Diameter (mm) |
Head/Wrench Size (mm) |
|||
|---|---|---|---|---|
| ANSI/ISO | DIN | JIS | DIN/ISO Heavy Hex |
|
| 4 | 7 | 7 | 7 | – |
| 5 | 8 | 8 | 8 | – |
| 6 | 10 | 10 | 10 | – |
| 7 | – | 11 | – | – |
| 8 | 13 | 13 | 12 | – |
| 10 | 16 | 17 | 14 | – |
| 12 | 18 | 19 | 17 | 22/21* |
| 14 | 21 | 22 | 19 | – |
| 16 | 24 | 24 | 22 | 27 |
| 18 | – | 27 | – | – |
| 20 | 30 | 30 | – | 34/32* |
| ANSI – American National Standards Institute ISO – International Organization for Standardisation DIN – Deutsches Institut fur Normung JIS – Japanese Industrial Standard * Indicates ISO standard. |
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Learn more about threaded joints.