Seiko Tmi Nh Caliber

Seiko Caliber NHxx Variation Differences

Seiko Tmi Nh Caliber

What is the difference between Seiko/TMI/SII “NH” calibers?

As of this post there are 10 calibers in the current line of NH “Basic Mechanical Series” movements. We will focus on the main 6 variations based on the NH35, information about the other four will be at the bottom of the page.

Mens size watches

  • NH35 (Seiko 4R35)
  • NH36 (Seiko 4R36)
  • NH37 (Seiko 4R37)
  • NH38 (Seiko 4R38)
  • NH39 (Seiko 4R39)
  • NH70

There are some differences between these overall similar movements but they are all based off of the original NH35 caliber which is based off of the NH25. The differences are mostly related to day/date/24 hour indicator. Please compare in the chart below. Did we miss anything? Please comment below.

Main Differences:

3 Hands Yes Yes Yes Yes Yes Yes
Date Yes Yes Yes No No No
Day No Yes No No No No
24 Hr Dial No No Yes No Yes No
Skeleton No No No No No Yes

Specs Comparison:

Origin Japan/Malaysia
Year Introduced 2011? Unknown  Unknown Unknown  Unknown  2017
Diameter 12”’ (27.40mm)
Casing Diameter 29.36mm  27mm
Height 5.32mm
Jewels 24
Power Reserve > 41 Hours
Beats Per Hour 21,600 vph (6 vibrations per second)
Lift Angle 53 degrees
Hacking? Yes
Hand-Windable? Yes
Winding Direction? Bi-directional
Seiko Diashock


Time Module claims that the NH calibers are rated for static accuracy of -20 ~ +40 under normal temperature conditions. All measurements are done without the calendar function, as well as within 10-60 minutes while fully wound.

Difference Between Crown Functions

As we see here, the main differences between the two calibers is that the NH35A is hackable and can be hand-wound. That means the crown operates differently:

 Crown Position NH35A NH36A NH37A NH38A NH39A NH70A
  • Clockwise: Manual Winding
  • Counterclockwise: Free (does nothing)
  • Clockwise: Nothing
  • Counterclockwise: Sets the date (quick set)
  • Clockwise: Sets the day
  • Counterclockwise: Sets the date (quick set)
  • Clockwise: Nothing
  • Counterclockwise: Sets the date (quick set)
Time Setting Time Setting Time Setting
Time Setting None None None

Which NH caliber movement does my watch have?

Unless the manufacturer installed a custom rotor, the caliber number should be engraved or stamped there. If it has a closed caseback or custom rotor, you can tell by looking at the complications on the dial. Of course, it’s always possible that the manufacturer made their own modifications or removed some features that didn’t correspond with the watch design (say for example they got a really good deal on 200 NH35A but the watch doesn’t have a date window, they could just use the NH35A without the date).

Which one better?

It really depends on what you need from a watch! If you like simple minimalist 3 hand watches, then the NH38A is for you. If you like have a 24 hour subdial, then go for a watch with the NH37A. Let the community know which caliber you prefer and why in the comments below…

Ladies and midsize NH calibers:

  • NH05
  • NH06
  • NH15
  • NH16


TMI aka Seiko Instruments markets the “NH” calibers as “Basic” Mechanical Series. They also have “NE” calibers that are marketed as “Premium” Mechanical Series.


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