Seiko (SII) Caliber NH37A

Manufacturer	Seiko
Caliber Number	NH37A (aka NH37)
Base Caliber	NH35A
Movement Type	Automatic
Jewels	24
Vibrations Per Hour	21,600 bph
Shock System	Diashock
Power Reserve	41 hours
Winding Direction	Bi-directional with one way clutch
Hacking?	Yes
Hand-Windable?	Yes
Diameter	27.40mm (outside) / 29.36mm (casing)
Height	5.32mm
Functions	Hours, minutes, central seconds, date calendar, 24 hour indicator
Country of Manufacture	Japan/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.

• For complete specs and drawings, see this pdf
• Parts catalogue for caliber NH37A
• Also see this thread: Seiko NH Caliber Comparison/Differences
• More watch models with the caliber NH35 here
• Difference between SII and TMI

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