Certina 13.20-770, Main spring
- Manufacturer: Prima, no: 135 D 21
- H: 1,35
- D: 5,5
- F: 0,065
- L: 210
Versions:
- 13-20: N: = 19.800, no mountings.
- 13-21: N: = 19.800, mounting threads.
- 13-22: N: = 21.600, mounting threads.
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