10 mm spanner
10.00 mm · 0.39 in
10 mm across the flats · fits a M6 hex head
The nearest imperial size
3/8″ is 9.52 mm — 0.48 mm smaller than 10 mm.
That is not close enough. 3/8″ is smaller than the 10 mm head, so it will not go on at all — which is the harmless failure of the two.
The numbers
| Across flats | 10.00 mm · 0.39 in |
| Nearest imperial | 3/8″ — 9.52 mm |
| Difference | 0.48 mm — not safe to substitute |
| Fits | M6 hex head |
Nearby metric sizes
| Size | mm | Nearest imperial | Gap |
|---|---|---|---|
| 7 mm | 7.00 | 1/4″ | 0.65 mm — do not |
| 8 mm | 8.00 | 5/16″ | 0.06 mm — swap |
| 9 mm | 9.00 | 3/8″ | 0.52 mm — do not |
| 10 mm | 10.00 | 3/8″ | 0.48 mm — do not |
| 11 mm | 11.00 | 7/16″ | 0.11 mm — swap |
| 12 mm | 12.00 | 1/2″ | 0.70 mm — do not |
| 13 mm | 13.00 | 1/2″ | 0.30 mm — do not |
Frequently asked questions
What is 10 mm in inches?
0.39 inches. The nearest imperial spanner is 3/8″ at 9.52 mm, 0.48 mm smaller.
Can I use 3/8″ instead of 10 mm?
Not safely. The gap is 0.48 mm. 3/8″ is smaller than 10 mm and simply will not go on.
What bolt does a 10 mm spanner fit?
A M6 hex head. The full metric thread chart gives the tapping drill and clearance hole for it too.