Table
Threads & pullers
Metric coarse and fine threads with pitch and tapping drill, plus the documented flywheel puller threads M17x1, M22x1.5, M26x1.5, M27x1.25.
Flywheel puller threads
The thread in the flywheel decides which puller fits. These four sizes are documented in the ELDI manufacturer data. For all other vehicles: measure the thread on the flywheel and identify it with the thread finder.
| Thread | Direction | Vehicles / ignition | ELDI puller |
|---|---|---|---|
| M17x1 | right hand | Piaggio Vespa Ciao, Bravo, SI | Flywheel puller M17x1 Piaggio Ciao |
| M22x1.5 | right hand | Bosch and Ducati ignitions: Zündapp, Hercules, Kreidler, Puch, KTM, DKW, Rixe, Sachs (small thread on the combination puller) | Flywheel puller M22x1.5 / M26x1.5 |
| M26x1.5 | right hand | Bosch and Ducati ignitions: Zündapp, Hercules, Kreidler, Puch, KTM, DKW, Rixe, Sachs (large thread on the combination puller) | Flywheel puller M22x1.5 / M26x1.5 |
| M27x1.25 | right hand | Ducati ignitions: Hercules, Garelli, Malaguti and other mopeds | Flywheel puller M27x1.25 |
Metric ISO thread
| Thread | Coarse pitch mm | Fine pitches mm | Tapping drill coarse mm |
|---|---|---|---|
| M3 | 0.5 | - | 2.5 |
| M4 | 0.7 | - | 3.3 |
| M5 | 0.8 | - | 4.2 |
| M6 | 1 | 0.75 | 5 |
| M7 | 1 | - | 6 |
| M8 | 1.25 | 1 | 6.8 |
| M10 | 1.5 | 1.25, 1 | 8.5 |
| M12 | 1.75 | 1.5, 1.25 | 10.2 |
| M14 | 2 | 1.5, 1.25 | 12 |
| M16 | 2 | 1.5 | 14 |
| M17 | - | 1 | - |
| M18 | 2.5 | 2, 1.5 | 15.5 |
| M20 | 2.5 | 2, 1.5 | 17.5 |
| M22 | 2.5 | 2, 1.5 | 19.5 |
| M24 | 3 | 2, 1.5 | 21 |
| M26 | - | 1.5 | - |
| M27 | 3 | 2, 1.5, 1.25 | 24 |
| M28 | - | 2, 1.5 | - |
| M30 | 3.5 | 2, 1.5 | 26.5 |
How to measure a thread
Measure the outside diameter across the thread crests with a vernier caliper. An M22 usually measures 21.8 to 22.0 mm.
Pitch with a thread gauge or a ruler: count ten threads, measure the length, divide by ten.
On female threads (flywheel) try a matching bolt, or measure the tapping drill diameter and read the table backwards.
Check the direction: a right hand thread tightens clockwise. Left hand threads occur on sprocket and clutch shafts.
Questions
Why do flywheels have fine threads?
A fine thread carries on more threads per unit of length and fits into thin-walled hubs. That is why M22x1.5, M26x1.5 or M27x1.25 are common, not the coarse thread.
Does M22x1.5 fit an M22x1 flywheel?
No. Same diameter, different pitch: the puller only grips on one thread and tears the thread out. Always check pitch and diameter.
What is the tapping drill?
The hole diameter a female thread needs before the thread is cut. For M8 coarse thread it is 6.8 mm.