Manufacturer | Seiko (SII, TMI) |
Caliber Number | NH38, NH38A |
Movement Type | Automatic, self-winding mechanical |
Diameter |
27.40mm |
Casing Diameter |
29.36mm |
Height |
5.32mm |
Jewels | Twenty-Four (24) |
Vibrations Per Hour |
21,600 bph, 3 Hz |
Lift Angle |
53 degrees |
Accuracy Rating |
-20~+40 sec/day average |
Power Reserve |
~41 hours |
Rotor Winding Direction |
Bi-directional (Seiko Magic Lever) |
Manual-Winding? |
Yes |
Anti-Shock System | Diashock |
Hand Count |
3 |
Functions | Central hours; central minutes; central sweeping seconds |
Notable Features |
True no-date, open balance wheel at 9:00 |
Hacking Seconds? | Yes |
Country of Manufacture | Japan/Malaysia (see below…) |
Known Brands |
Various Invicta, Gruppo Gamma Venturo Field III (Add your watch in the comments below…) |
The Seiko caliber NH38A is a 3-hander “no-date” automatic watch movement with 24 jewels. It is a true no-date without a phantom date crown position. Many watch enthusiasts would agree that that the NH38 is the definition of a solid, no-frills workhorse movement.
The NH38 series has an open balance wheel at 9:00 on the dial side. However, many watch brands do not make use of this design feature and choose to cover it with a solid dial.
Some of the topics covered in this caliber listing:
What is the difference between the NH38A and NH35A?
is very similar to the popular caliber NH35A in which is it based on, with the main difference being that the NH38A is essentially the no-date version of the widely used NH35A/NH36A. Unlike the NH35A, the NH38A is a basic three hand watch and does not have a day or date complication. Another difference is that the NH38A is partially skeletonized with an open balance wheel, viewable from the front side of the watch face.
Note: due to the NH35A being more ubiquitous and easy to obtain, you may find examples of watch brands offering a no-date style watch, but using the the NH35A with a datewheel instead of the NH38A. If you want a true no-date, you should not settle for an NH35A powered watch that simple has the date covered by a solid dial.
Accuracy Rating:
Time Module (TMI) claims an accuracy rating of -20~+40 seconds per day in normal operating conditions.
Japan or Malaysia or…?
The complete Japanese-made caliber number is NH38A3J. For the Malaysia variant, the official number is NH38A3M. Regardless of where the movement was made, these longer numbers are mostly for ordering purposes and not found anywhere on the movement itself. Most are not marked with a country of origin… so, technically, who knows!
Also, despite the official documentation mentioning Japan or Malaysia signed rotors, Caliber Corner has never actually seen one marked with the country of origin from the factory.
Replacement Prices:
At the time of this caliber listing, replacement prices for the NH38 were found in the range of $34.99 to $55.00 USD. You can find replacements here.
Other examples of this movement:
Below is an NH38 found in a Gruppo Gamma Field III microbrand watch:
The large photo below is of a Seiko NH38A movement in an Invicta 22744 watch.
Image above submitted by Nathaniel B.
NH38A Tech Sheets/Technical Drawings (pdf):
Caliber Commentary:
From a post on the @calibercorner Instagram page…
View this post on Instagram
Additional Resources:
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