Table
Across flats sizes
Which across flats size belongs to which thread: hexagon to ISO 272 and old DIN, hexagon socket to DIN 912. From M3 to M30.
16 rows
| Thread | AF hexagon ISO | AF hexagon old DIN | Hexagon socket |
|---|---|---|---|
| M3 | 5.5 | 5.5 | 2.5 |
| M4 | 7 | 7 | 3 |
| M5 | 8 | 8 | 4 |
| M6 | 10 | 10 | 5 |
| M7 | 11 | 11 | - |
| M8 | 13 | 13 | 6 |
| M10 | 16 | 17 | 8 |
| M12 | 18 | 19 | 10 |
| M14 | 21 | 22 | 12 |
| M16 | 24 | 24 | 14 |
| M18 | 27 | 27 | 14 |
| M20 | 30 | 30 | 17 |
| M22 | 34 | 32 | 17 |
| M24 | 36 | 36 | 19 |
| M27 | 41 | 41 | 19 |
| M30 | 46 | 46 | 22 |
ISO or DIN: why there are two sizes
The old DIN 931/933 used across flats 17 for M10, 19 for M12 and 22 for M14. ISO 272 reduced these sizes to 16, 18 and 21. On mopeds from the 1960s to the 1990s you will mostly meet the old sizes, on new replacement bolts the ISO sizes. A set with 16, 17, 18, 19, 21 and 22 covers both.
Special sizes on two-wheelers
- Spark plugs: 21 mm (classic 14 mm plugs with a 20.8 hexagon) or 16 mm (modern plugs). ELDI offers the 21 mm spark plug spanner.
- Wheel hubs: ring nuts with a hook spanner, 17 mm lock nut on the wheel hub spanner.
- Flywheel nuts and clutch nuts: usually large fine threads, size as per the manual.
Questions
What across flats size does M8 have?
13 mm, both to ISO and to old DIN. For M8 there was no change.
What is the across flats size on a hexagon socket?
The distance between the parallel faces of the hexagon socket, that is the size of the hex key. M6 needs 5 mm, M8 6 mm, M10 8 mm.