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Seiko (TMI) NH38 Automatic Movement - Open Heart

Genuine SEIKO NH38 Movement with an open-heart display at 9 o'clock crown position. This movement is designed for dials with open-heart window

The TOP choice for movement swap with a direct view of the escapement from the watch face. Appreciating the beauty and intricacy of a mechanical movement.

With two available options:

    Hugely improved on the accuracy! These are regulated by certified watchmakers from 0 to +8 seconds per day.
    Fresh out of the factory defaults without any regulation. Accuracy are in accordance to SEIKO's specification of -20 to +40 seconds per day.
Learn how to upgrade your movement, click here

IMPORTANT: Movement upgrade/swap is ONLY recommended for individuals with the right skillsets and experience. Lucius Atelier is not responsible for any damage to the movement during the fitting process. All movements passed Time Module Inc. (TMI) QC prior to shipping are guaranteed to be a fully functional movement. Given the high degree of DIY nature and Seiko's trade practices, unfortunately, we are unable to accept any returns.

Made by Time Module Inc. (TMI)


    1. Manufacturer Time Module Inc. (TMI)
    2. Caliber NH38A
    3. Movement Type Automatic, Mechanical
    4. Hand Height Type M
    5. Movement Diameter 27.40mm
    6. Casing Diameter 29.36mm (with dial holding spacer)
    7. Movement Height 5.32mm
    8. Jewels 24 jewels
    9. Beats Per Hour 21,600 vph (6 vibrations per second)
    10. Special Feature Open-Heart (Display of escapement)
    11. Hacking Yes
    12. Manual Winding Yes
    13. Winding Direction Clockwise
    14. Power Reserve More than 41 Hours
    15. Hands Fitting Size H:1.5mm, M:0.88mm, S:0.2mm
    1. Movement x1
    2. Full length threaded stem x1
    3. Dummy stem & plastic crown x1
    1. To learn how to upgrade your movement, search YouTube: NH36 Movement Upgrade

Customer Reviews

Based on 18 reviews
Erik S. (Schiedam, NL)
Using this mod part for: Aftermarket case
Doe it need regulation?

Happy to have this from Lucius Atelier

Beat error 0.0
+2 seconds a day

First time I did not have to regulate it myself.

Very pleased with this one.

Jens (Hamburg, DE)
Using this mod part for: Aftermarket Explorer 1 Case
Regulated NH38A

Absolutely no problem here. Paid via PP and i had the movement at home within days. Any time again with that service :)

Adrien G. (Lyon, FR)

Great movement, it runs at +2s/day.

Sean B. (Sweet Home, US)
Using this mod part for: SKX013 aftermarket field watch case.
Great movement keeps great time

Order this for my latest build. The dial has not date hand and I hate ghost dates, so this works perfectly. The movement arrived quickly and keeps great time. The movement is quiet and works great and most angles. Love it.

C.M. (Melbourne, AU)
Using this mod part for: Aftermarket
Awesome mod!

I bought this watch as a birthday present to me and I’m super happy with it! I chose the NH38 movement which works well give the dial has no date. The dauphine GS hands complement the watch greatly and the watch case is of very good quality also. The clasp of the bracelet I do not like however and struggle to open. In future this should hopefully be taken into account. The customer service was 10 out of 10 and I would happily buy from this seller again! Overall I am 100% happy with the purchase!

Using this mod part for: LA 36mm Explorer V2 case
Initial doubts conquered by daily wear

When I first recieved the assembled watch, I immediately fully wound it, let it run 20 minutes, and then popped it on my timegrapher. I was excited to have the painstaking work already done. Initially results were not promising, as in the dial up position it was running +17 (tool was set up per Seiko spec). In the other positions it measured between -1 to +10. However, after wearing the watch for almost a week, it has only gained 8 seconds. So in practical use it's a +1 second/day movement, and that is amazing! I am happy enough, I am getting a regulated NH36 movement for another watch.

Matsuzaki H. (Setagaya-ku, JP)
Using this mod part for: Aftermarket cases
Good watch

I like this watch very much.
I ordered a stainless steel case.

Cameron (Melbourne, AU)

Regulated and accurate as claimed. Fast shipping and a pleasure to to business with, arrived with a personally written card - thank you again Adriel!

Billy R. (Fredericksburg, US)
Installed in built watch, running great!

Ordered this regulated movement with the 36mm Explorer style case, dial and hands. As of writing this review the movement is running great! Over 6 positions avg +3 sec/day with a total deviation (range) of 15 secs. avg Beat error of .3ms with total deviation of .6ms; as recorded via time grapher.

Sean K. (Sidney, CA)
Using this mod part for: Aftermarket cases
Great movement

Again as always great customer service and quality products. Movement came very well timed. Cheers!