Hex / Allen Key Size Chart (SAE & Metric) | HandySkook
Hex / Allen Key Size Chart (SAE & Metric)
A hex (Allen) key size chart listing SAE (inch) and metric (mm) sizes side by side — for the set screws, furniture and bikes that use them.
Hex key sizes
| SAE (in) | Metric (mm) |
|---|---|
| 0.028 | 0.7 mm |
| 0.035 | 0.9 mm |
| 1/16 | 1.5 mm |
| 5/64 | 2 mm |
| 3/32 | 2.5 mm |
| 1/8 | 3 mm |
| 5/32 | 4 mm |
| 3/16 | 5 mm |
| 1/4 | 6 mm |
| 5/16 | 8 mm |
| 3/8 | 10 mm |
| 1/2 | 13 mm |
Hex keys are sized by the flat-to-flat width. SAE and metric are close but not identical — a too-small key will round the socket, so match exactly when you can.
Frequently asked questions
What metric hex key is closest to 1/8 inch?
3 mm is the closest metric Allen key to 1/8 in (3.18 mm), but they are not identical.
How are hex keys measured?
By the flat-to-flat width of the hex, in either inches (SAE) or millimeters (metric).
- Choosing a selection results in a full page refresh.
