Seiko Caliber Nh37

Seiko (SII) Caliber NH37A

Seiko SII Caliber NH35

Caliber NumberNH37A (aka NH37)
Base CaliberNH35A
Movement TypeAutomatic
Vibrations Per Hour
21,600 bph
Shock SystemDiashock
Power Reserve
41 hours
Winding Direction
Bi-directional with one way clutch
Diameter27.40mm (outside) / 29.36mm (casing)
FunctionsHours, minutes, central seconds, date calendar, 24 hour indicator
Country of ManufactureJapan/Malaysia
Known Brands
AVI-8 Lancaster Bomber (add more in the comments below)




The Seiko/TMI/SII caliber NH37 is a hand-windable, hacking variation of the widely popular caliber NH35A – one of the world’s most popular automatic movements and is widely available in many affordable/microbrand watches. In comparison, the NH37A listed here has an additional complication: a 24 hour indicator. This is the only difference between the NH35 and NH37.

Crown Position Functions:

0 (against the case): Clockwise = Manual Winding / Counterclockwise = Nothing
1 (pulled out one click): Clockwise = nothing / Counterclockwise = Date setting
2 (pulled out two clicks): Time setting clockwise and counterclockwise

More Information

Interesting Note: Time Module aka Seiko Instruments labels the NH calibers as part of the “Basic” Mechanical Series. They also have NE calibers that are labeled as “Premium” Mechanical Series.

Seiko Caliber Nh37

Seiko Caliber Nh37a

Seiko Nh37a Gears

Seiko Nh37a Anti Shock

The example above is from an AVI-9 Lancaster Bomber here.

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Frederik de Haan
Frederik de Haan
1 year ago

These NH XX movements are true marvels in their own right !

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