16 mm spanner
16.00 mm · 0.63 in
16 mm across the flats · fits a M10 (ISO 4017) hex head
The nearest imperial size
5/8″ is 15.88 mm — 0.13 mm smaller than 16 mm.
That is close enough to be interchangeable. 0.13 mm is well inside the manufacturing tolerance of the fastener, and the two will feel identical in use.
The numbers
| Across flats | 16.00 mm · 0.63 in |
| Nearest imperial | 5/8″ — 15.88 mm |
| Difference | 0.13 mm — interchangeable |
| Fits | M10 (ISO 4017) hex head |
Nearby metric sizes
| Size | mm | Nearest imperial | Gap |
|---|---|---|---|
| 13 mm | 13.00 | 1/2″ | 0.30 mm — do not |
| 14 mm | 14.00 | 9/16″ | 0.29 mm — do not |
| 15 mm | 15.00 | 9/16″ | 0.71 mm — do not |
| 16 mm | 16.00 | 5/8″ | 0.13 mm — swap |
| 17 mm | 17.00 | 11/16″ | 0.46 mm — do not |
| 18 mm | 18.00 | 11/16″ | 0.54 mm — do not |
| 19 mm | 19.00 | 3/4″ | 0.05 mm — swap |
Frequently asked questions
What is 16 mm in inches?
0.63 inches. The nearest imperial spanner is 5/8″ at 15.88 mm, 0.13 mm smaller.
Can I use 5/8″ instead of 16 mm?
Yes. They are 0.13 mm apart, which is inside the tolerance of the fastener itself — these two are interchangeable in practice and most mechanics never notice they own both.
What bolt does a 16 mm spanner fit?
A M10 (ISO 4017) hex head. The full metric thread chart gives the tapping drill and clearance hole for it too.