9/16″ spanner
14.29 mm · 0.56 in
9/16″ across the flats
The nearest metric size
14 mm is 14.00 mm — 0.29 mm smaller than 9/16″.
That is not close enough. 14 mm is smaller than the 9/16″ head, so it will not go on at all — which is the harmless failure of the two.
The numbers
| Across flats | 14.29 mm · 0.56 in |
| Nearest metric | 14 mm — 14.00 mm |
| Difference | 0.29 mm — not safe to substitute |
Nearby imperial sizes
| Size | mm | Nearest metric | Gap |
|---|---|---|---|
| 7/16″ | 11.11 | 11 mm | 0.11 mm — swap |
| 1/2″ | 12.70 | 13 mm | 0.30 mm — do not |
| 9/16″ | 14.29 | 14 mm | 0.29 mm — do not |
| 5/8″ | 15.88 | 16 mm | 0.13 mm — swap |
| 11/16″ | 17.46 | 17 mm | 0.46 mm — do not |
Frequently asked questions
What is 9/16″ in millimetres?
14.29 mm. The nearest metric spanner is 14 mm — 0.29 mm smaller.
Can I use 14 mm instead of 9/16″?
Not safely. The gap is 0.29 mm. 14 mm is smaller than 9/16″ and simply will not go on.
Where is 9/16″ used?
Imperial spanner sizes are "across flats" measurements and are still standard on American vehicles, plumbing and older machinery everywhere.