Seiko (SII) Caliber NH38A Watch Movement

Manufacturer	Seiko (SII, TMI)
Caliber Number	NH38A
Movement Type	Automatic, self-winding mechanical
Diameter	27.40mm (outside) / 29.36mm (casing)
Height	5.32mm
Jewels	24
Vibrations Per Hour	21,600 bph
Anti-Shock System?	Yes
Power Reserve	41 hours
Rotor Winding Direction	Bi-directional (Seiko Magic Lever)
Functions	Central hours; central minutes; central sweeping seconds
Hacking Seconds?	Yes
Notable Features	No-Date, open balance wheel
Country of Manufacture	Japan/Malaysia
Known Brands	Various Invicta, Gruppo Gamma Venturo Feild II (Add your watch in the comments below…)

The Seiko caliber NH38A is very similar to the popular caliber NH35A.The NH38 series is often found with an open balance wheel at 9:00 on the dial. The NH38A is a 3-hander “no-date” movement. It is a true no-nate without a phantom date crown position.

Some of the topics covered in this caliber listing:

What is the difference between the NH38A and NH35A?

The NH38A is the no-date version of the NH35A. 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 skeltonized with an open balance wheel.

Accuracy Rating:

Time Module (TMI) claims an accuracy rating of -20~+40 seconds per day.

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!