Specs and Measurements of Seiko (SII) Caliber NH34A / 4R34

The New GMT Movement from Seiko / TMI /SII

Movement diagram of Seiko NH34A / 4R34

The NH34 or also known as NH34A is a new movement from Seiko / TMI / SII that is becoming increasingly popular, due to its budget friendly nature and its ability to tell time in a second time zone (also known as a GMT movement). Depending on the source, this movement can also be named as 4R34, which is an identical movement with a different naming. Here is the basic measurements and specification of NH34A:

Basic measurements

• Number of jewel: 24 jewels

• Outside diameter: 27.40 mm

• Lignes: 12”’

• Casing diameter: 29.36 mm (with dial holding spacer)

• Total height: 5.32 mm

Specification

Time indication

• 3 Hands (hour, minute, second)

• Date calendar

• 24 hour hand

Basic functions

• Manual winding

• Automatic winding (Bi-directional rotor winding via Magic Lever)

• Stop-second / hacking second

• Quick date change

• Second time zone setting (aka GMT function)

Technical specification

• Frequency: 21,600 vibrations per hour (vbh)

• Factory rated accuracy: - 20 ~ + 40 seconds per day

• Lift angle: 53 degrees

• Power reserve: 41 hours

Similarities with NH35 Movement

Notice the extra step on the central post: this will affect its compatibility with NH35a movement

As veteran modders might notice, the specs and measurements are largely the same as those of a NH35 movement, the only noted addition being the GMT function. Does that mean you can simply do an GMT upgrade to your existing Seiko watch? Well, yes and no. The addition of GMT function means alteration to the hand post. If you account for this difference, the upgrade can indeed be carried out. We have written a detailed breakdown of the differences between the two movements, and how they affect their mod compatibility. Be sure to check it out!

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