7/8″ spanner
22.22 mm · 0.88 in
7/8″ across the flats
The nearest metric size
22 mm is 22.00 mm — 0.22 mm smaller than 7/8″.
0.22 mm is a marginal fit: usable on a fastener that turns freely, and a poor idea on one that is seized or soft.
The numbers
| Across flats | 22.22 mm · 0.88 in |
| Nearest metric | 22 mm — 22.00 mm |
| Difference | 0.22 mm — marginal |
Nearby imperial sizes
| Size | mm | Nearest metric | Gap |
|---|---|---|---|
| 3/4″ | 19.05 | 19 mm | 0.05 mm — swap |
| 13/16″ | 20.64 | 21 mm | 0.36 mm — do not |
| 7/8″ | 22.22 | 22 mm | 0.22 mm |
| 15/16″ | 23.81 | 24 mm | 0.19 mm |
| 1″ | 25.40 | 24 mm | 1.40 mm — do not |
Frequently asked questions
What is 7/8″ in millimetres?
22.22 mm. The nearest metric spanner is 22 mm — 0.22 mm smaller.
Can I use 22 mm instead of 7/8″?
Marginally. 0.22 mm is enough to feel loose on a tight fastener and enough to round a soft one. It will work on something that is not seized; it is not what you want on something that is.
Where is 7/8″ used?
Imperial spanner sizes are "across flats" measurements and are still standard on American vehicles, plumbing and older machinery everywhere.