An NHXX Movement is the beating heart of modified Seiko watches, this page covers a number of the other calibre included within Seiko mods. The calibres (movements) included in this guide are the NH38, NH39, NH70, NH71 and NH72. We have used NHXX in places to signify any one of these movements.

These varying calibres found came to the market around 2016. They are built on the base calibre of the 4R35 which came into production in 2011. It is argued by many that this movement rivals the Swiss movements in lower priced Swiss watches, on durability and accuracy, as well as long term operation. provides further information on each individual movement’s operations, but suffice to say, the complications vary and there are options for Open Heart and Skeleton watches which are contained within this guide. None of these movement have any complications and they all share the same operating procedure.

  • NH38 – Open Heart
  • NH39 – Open Heart & Sub Dial @ 10:30
  • NH70 – Skeleton Steel Finish
  • NH71 – Skeleton Gold Finish
  • NH72 – Skeleton Black Finish

Information and Specifications

The Calibres (movements) are Japanese, produced by Seiko Instruments Inc. aka SII, Time Module Inc. aka TMI). These beat at 21,600 beats per hour. This means the second hand moves six times per second to create the sweeping movement.

The tech data suggests that, worn daily for 8-10 hours, and at a temperature range of between 5°C and 35°C, the Cal. NHXX (movement) has an accuracy of +45 and -35 seconds per day. In practice, this is very far from the mark, as these watches movements can be regulated to produce a more precise performance.

The movement has a number of features such as ‘hand-winding’, useful if your wear watches in rotation. It also features hacking of the second hands, effectively stopping the second hand so you can synchronise watches like you are in an 80’s action movie! Operational instructions can be found here.

Tech Spec NHXX Movement

Movement TypeAutomatic, self-winding mechanical
Casing Diameter29.36mm
Vibrations Per Hour21,600 bph
Lift Angle53 degrees
Shock SystemDiashock
Power Reserve41 hours
Rotor DirectionBi-directional winding (Magic Lever)

Calibre Various Winding System

This movement features automatic winding with the manual winding mechanism.

Time Display on the Cal. NHXX (Movement)

The time display on these calibres use a three hand display, located in the in the centre of the dial. The exception to this is the NH39 which has an additional forth hand (24 hour) on a sub dial at 10:30.

Complications of the Cal. NHXX (Movement)

There are no additional complications, these movements display the time only, although have their own aesthetics which more than make up for the lack of complications, allowing Seiko modders to create beautiful and affordable time pieces.

If you’ve found this guide helpful, be sure to explore our collection of other informative guides at We offer a wealth of resources to assist you in your modding journey.