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Seiko (TMI) NH38 Automatic Movement - Open Heart
$190 SGD - $240 SGD
The open-heart showpiece.
Genuine Seiko NH38 automatic movement with an open-heart display, crown at 3 o'clock. A no-date, three-hand movement designed to pair with open-heart dials so the balance wheel is visible through a window in the dial. The escapement on show, from the front.
Two accuracy grades. One genuine Seiko caliber, QC-passed by TMI.
Pick Regulated for watchmaker-tuned precision, or Non-Regulated for Seiko factory spec. Every unit is a genuine Time Module Inc. movement, tested functional before it ships.
Watch it beat, from the front.
The NH38 is built so the oscillating balance wheel shows through an aperture in an open-heart dial, no display caseback needed. A live view of the escapement on the dial side.
Regulated or non-regulated.
Choose Regulated and a certified watchmaker tunes it to 0 to +8 seconds/day before it ships. Choose Non-Regulated for factory-default accuracy of -20 to +40 seconds/day per Seiko's spec. Same movement, your call on precision.
Hacking and hand-winding.
Both built in. The seconds hand stops when you pull the crown for precise time-setting, and you can manually wind it. The popular reason modders upgrade from older 7S26/7S36 calibers.
No date, clean three-hand.
A pure three-hand movement with no date complication, ideal for clean dials and open-heart faces. Ships with a full-length threaded stem and a dummy stem with plastic crown.
How the NH family compares
| Caliber | Complication | Crown Position | Version |
|---|---|---|---|
| NH34 | GMT + Date | 3 or 4 o'clock | White |
| NH35 | Date | 3 or 4 o'clock | Black White |
| NH35 | Date · 6 o'clock dial | 3 or 4 o'clock | Black White |
| NH36 | Day + Date | 3 o'clock only | Black White |
| NH36 | Day + Date | 4 o'clock only | Black White |
| NH38 · THIS MOVEMENT | Open Heart (no date) | 3 or 4 o'clock | View |
| NH70 / 71 / 72 | Skeleton (no date) | 3 or 4 o'clock | NH72 |
Most NH movements fit either a 3 or 4 o'clock crown — the stem threads either way and the date disc isn't affected. The NH36 is the exception: its day wheel is pre-aligned for one crown position, so pick the standard (3 o'clock) or the 4 o'clock version to match your case. Every caliber shares the same 24-jewel automatic platform, 21,600 vph beat rate, and 41+ hour power reserve. Click any version to go straight to that product.
For experienced modders only
Movement swapping is recommended only for individuals with the right skills and experience. Every movement passes Time Module Inc. (TMI) quality control before shipping and is guaranteed fully functional on arrival. Given the DIY nature of modding and Seiko's trade practices, movements cannot be returned once shipped. We are not responsible for damage incurred during fitting.
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- Manufacturer Time Module Inc. (TMI)
- Caliber NH38A
- Movement Type Automatic, Mechanical
- Hand Height Type M
- Movement Diameter 27.40mm
- Casing Diameter 29.36mm (with dial holding spacer)
- Movement Height 5.32mm
- Jewels 24 jewels
- Beats Per Hour 21,600 vph (6 vibrations per second)
- Additional Function None (3-hand, no date)
- Hacking Yes
- Manual Winding Yes
- Winding Direction Clockwise
- Power Reserve More than 41 hours
- Accuracy (Regulated) 0 to +8 seconds/day
- Accuracy (Non-Regulated) -20 to +40 seconds/day
- Hands Fitting Size H: 1.5mm, M: 0.88mm, S: 0.2mm
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Where this movement fits
- Hand height Type M (standard) — confirm your case accepts Type M before fitting
- Our cases All Ultra Thin Edition cases (TYPE M)
- Dial 28.5mm Seiko Mod dials — no-date / open dials
- Hands NH-series compatible
Pair the NH38 with an open-heart dial to use the cut-away view, or any no-date dial for a clean three-hander. Fits every Ultra Thin Edition case that takes a TYPE M movement.
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- 1x NH38 movement
- 1x Full-length threaded stem
- 1x Dummy stem with plastic crown
All photos showing movements fitted with dials, hands, or cases are for illustration only and are not included with the movement purchase.
Questions, Answered
Everything worth knowing before you build.
What is the NH38 open heart, and which dial does it need?
Will the NH38 fit a 3 or 4 o'clock crown case?
What's the difference between Regulated and Non-Regulated?
Is this a Type M or Type L movement, and does it matter?
Can I return a movement if my mod doesn't work out?
NH34 vs NH35 vs NH36 vs NH38 vs NH70 — what is the actual difference?
Customers praised this automatic movement for exceptional accuracy, with many reporting +2 seconds/day performance. "Regulated and accurate as claimed" with "beat error 0.0," shoppers appreciated not needing to regulate it themselves. Quality is "OEM" level, works well for no-date builds. One customer noted price could be lower elsewhere.
- Beat error 0.0, +2 seconds a day. First time I did not have to regulate it myself.
- Genuinely impressed with the quality of this build.
- Regulated and accurate as claimed. Fast shipping and a pleasure to do business with.
Shipping (positive)Accuracy (positive)Service (positive)Quality (positive)Movement (positive)
S
Using this mod part for: SKX013 aftermarket field watch case.
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
Using this mod part for: Aftermarket
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!
S
Using this mod part for: LA 36mm Explorer V2 case
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.
S
Using this mod part for: Aftermarket cases
Again as always great customer service and quality products. Movement came very well timed. Cheers!
W
Using this mod part for: Aftermarket case 36mm
Nice movement and fast delivery 👍
M
Using this mod part for: I’m building a custom bronze divers with no day or date complications.
Very good personal service. This is my first purchase but it certainly won’t be my last!
T
Using this mod part for: Skx005
This is a verry nice movement
A
Great to be able to buy a properly-regulated movement! Lucius are always great to deal with also.
B
Using this mod part for: Explorer Case 39mm
Got the regulated NH38 with the explorer case and 1016 dial. As the owner of a 50th anniversary Seamaster and Explorer 2 16570, I am genuinely impressed with the quality of this build. Already looking for the next purchase.
M
Using this mod part for: Aftermarket case
First time buyer, smooth transaction and fast shipping.
Not fitted into my latest build yet as I’m still gathering some more parts. But overall great service will be buying again. Thank you!
K
OK price, you can save a few bucks elsewhere, but I went with this to guarantee fitment with the ultra thin LA cases.
E
Using this mod part for: Aftermarket case
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.
J
Using this mod part for: Aftermarket Explorer 1 Case
Absolutely no problem here. Paid via PP and i had the movement at home within days. Any time again with that service :)
A
Great movement, it runs at +2s/day.
M
Using this mod part for: Aftermarket cases
I like this watch very much.
I ordered a stainless steel case.
C
Regulated and accurate as claimed. Fast shipping and a pleasure to to business with, arrived with a personally written card - thank you again Adriel!
W
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.
D
Using this mod part for: Seiko
I fell in love with other this watch, to be honest the pictures on the site look stunning but nothing compares in person. This is my favorite watch now.. and shout out to adriel , my bro has the best service.
P
Super fast delivery to Belgium! Couldn’t be happier!
R
Using this mod part for: Unimatic U1
Prompt shipping. Nicely regulated movement. Superb customer service and communication. It was a delight to do business with Lucius Atelier.
K
Using this mod part for: Full build
OEM quality(because it’s a genuine Epson/Seiko movement). I’m glad that Adriel offers these, as they can be tough to source for no-date builds.
B
Using this mod part for: Skx007
Purchased NH 38 movement and open heart dial. Everything looks and works great.
U
Is the regulated version coming back in stock?
Hi Thanh,
Thanks for expressing interest in our mod parts!
The regulated NH38 version won’t be restocked at the moment. I’m expecting it to return in about 4–6 months, but there’s no confirmed date yet.
If you’d like, I can let you know once it’s back.
Best regards,
Adriel
Lucius Atelier | SEIKO Mod Parts
U
Are there plans to restock the regulated version of this?
Hi,
Thanks for your interest in our NH38 Open Heart movements!
At the moment, there are no plans to restock the regulated version.
If this changes, I’ll be sure to update the product page accordingly.
Thanks again for reaching out, and feel free to let me know if you have any other questions.
Best,
Adriel
Lucius Atelier | SEIKO Mod Parts
S
Can this movement be used on a 3.8 o’clock or 4 o’clock case?
Hi Pearleen,
Thank you for expressing interest in our mod parts!
Yes, the NH38 movement can be used in a 3.8 o’clock or 4 o’clock case. However, please note that since this is an open-heart movement, the position of the open-heart window will be tilted according to the angle shift of the movement within the case.
Let me know if you have any other questions—I’d be happy to assist!
Best regards,
Adriel
Lucius Atelier | SEIKO Mod Parts
A
I'm new to watch modding and looking to make an open-heart watch — what does Non-Regulated vs Regulated mean when considering to buy this NH38 movement?
Hello OptimusDiaz!
Thanks for expressing interest in our mod parts!
>> what does Non-Regulated vs Regulated mean when considering to buy this NH38 movement?
• REGULATED - Accuracy from 0 to +8 seconds per day
• NON-REGULATED - Accuracy are in accordance to SEIKO's specification of -20 to +40 seconds per day.
Hope this helps. Let me know if you have anymore questions.
Cheers,
Adriel
