The Seiko NH Series, Explained

What the whole family has in common

Every full-size NH caliber - the NH3 group and the NH7 skeletons - is the same movement with a different top layer. TMI's product pages, and its technical documentation as recorded by the caliber reference, give the same core figures for all of them:

• 12 lignes: 27.40mm across, 29.36mm with the plastic dial-holding spacer that most of them ship with, and 5.32mm tall. That height is why NH-powered watches are rarely thin; a Miyota 9015 is 3.90mm for comparison.
• 24 jewels and 21,600 vibrations per hour - six ticks a second, the slower of the two common beat rates. Beat rate explained covers what that trades and the jewels guide what the count is actually counting.
• About 41 hours of running time from a full wind. Take it off Friday night and it has stopped by Sunday. See power reserve explained.
• -20 to +40 seconds a day as TMI's static rating, measured within 10 to 60 minutes of a full wind and with the calendar not engaged. It is a wide band, and it is normal at this price.
• A stop-second device - the seconds hand halts when you pull the crown all the way out, so you can set the watch to the second. Hacking, in other words, on every current member of the family.
• Hand winding, clockwise, with a full wind at roughly 55 turns of the crown. You cannot overwind it.
• Bidirectional automatic winding through Seiko's Magic Lever, plus Diashock shock protection. Country of origin is published as "Japan or Malaysia" - more on that below.

The caliber map

The differences are almost entirely about what shows on the dial. TMI's NH3 line-up lists six models; the NH7 line-up adds three skeletons in three finishes; the two small NH0 calibers are a different size altogether.

There is no accuracy, reserve, beat-rate or jewel-count difference between any of the 12-ligne calibers. Choosing an NH36 over an NH35 buys you a day window; choosing an NH70 buys you a view of the movement, and because it is made to run without a dial, it has no dial spacer and cases at 27mm rather than 29.36mm. The NH7 trio differ only in plating: the NH70 is nickel-plated silver, the NH71 gilt, and the NH72 - added around June 2022 - a ruthenium gray (TMI's "Ruthenium Grey"). Pick the dial layout you want; the engine underneath is the same.

Two calibers on that table deserve a caveat. TMI's line-up page names the NH38 and NH39 in its selector but did not render a specification block for either when we read it, so their rows rest on the caliber reference rather than on a TMI page. And the NH37's 24-hour subdial has no setting position of its own - the caliber reference lists crown position one as doing nothing clockwise on an NH37 - so it is a 24-hour read-out of the main time, useful as a day/night indicator, not the independently settable GMT hand of the NH34. If you want a real second time zone under $500, the GMT roundup is built around the 4R34, and the NH34 is the same movement.

NH versus 4R: same movement, different badge

The rule is simple: the 4R calibers are what Seiko puts in its own watches; the NH calibers are the same movements sold to everyone else. NH35 is the 4R35, NH36 is the 4R36, NH34 is the 4R34, NH70 is the 4R71. The caliber reference's wording is "basically an unbranded version", and that is the honest summary - a Seiko 5 Sports and a $300 microbrand diver are running the same architecture.

Three real differences do exist between the two names, and all three generate forum arguments:

• The accuracy figure. TMI rates the NH calibers at -20/+40 seconds a day. Seiko rates the 4R35 and 4R36 at -35/+45. Nothing inside is different - TMI's number is a static bench figure taken shortly after a full wind with the calendar off, while Seiko's is a claim for normal daily wear on the wrist between 5°C and 35°C. Seiko is describing a harder test, not a worse movement. Automatic watch accuracy explains why the on-wrist number is the one that matters.
• The jewel count. The NH35A is a 24-jewel movement and its rotor says so. Seiko's current 4R35B is engraved 23 jewels - Seiko's own service arm confirmed the 23 to the caliber reference after years of tech sheets saying 24 - and the 4R71 is likewise 23 against the NH70A's 24. The 4R36A stays at 24. One jewel changes nothing you can feel; it just explains why the Cocktail Time and the SRPF03 say 23 on the dial while a microbrand NH35 says 24.
• Where it was made. The 4R calibers are recorded as made in Japan. TMI publishes the NH family as "Japan or Malaysia", and the caliber reference notes that a large share of current NH rotors carry no country of origin at all, which TMI has not explained. A "Japanese movement" line on a microbrand listing is therefore a statement about the design, not necessarily about the factory.

Where it came from: the 7S26 and the NH25

The NH3 family is not a clean-sheet design. Seiko's own technical wording for the 4R35A is that it was "developed based on Cal. 7S series and Cal. 6R series design" with two additions: a manual winding function and a second hand stop function. The base is the 7S26 of 1996 - 21 jewels, the same 21,600 vph and roughly 41 hours, a hair thinner at 4.9mm, and famous for doing neither of those two things. The 7S26's unbranded twins were the NH25 (date) and NH26 (day-date), and TMI's own sheets state plainly that they have no manual winding function and no hack lever.

The 4R35/4R36 and the NH35/NH36 arrived around 2011 - the earliest NH35A documentation the caliber reference could find is dated February 2011 - and they replaced the 7S line in Seiko's catalog over the following years. That is the whole story behind the Seiko 5 changeover: the SNK809 and the old SKX are 7S26 watches that will never hack or hand-wind, and the 5 Sports that replaced them is a 4R36 that does both. Hacking and hand-winding explained covers whether that upgrade is worth paying for.

It also explains the single most common piece of misinformation about the family. Because the Invicta Pro Diver has shipped with the NH25A and, in later production, the NH35A, owners of the newer watch report that their "NH25 hacks and hand-winds". It does not; they have an NH35. The letters matter.

The letter on the end

NH35A and NH35 are the same thing. The trailing letter is the generation: A is the first version, and a B would mean TMI changed the parts. That has happened on the Seiko side - the 4R35B replaced the 4R35A with new, non-interchangeable parts (Seiko's sheets note the reserve moving from 41 to 40 hours and the lift angle from 52 to 53 degrees) - but at the time of writing only the NH35A exists. Talk of an "NH35B" that circulated in early 2026 is, per the caliber reference, speculation from people confusing it with Seiko-only calibers. If you see NH35B on a listing, ask what they mean.

Why it is in everything, and what it costs

Microbrands did not settle on the NH35 because it is the best movement at the price. They settled on it because it is a real Seiko-group caliber that hacks, hand-winds and winds both ways; because it is sold openly to anyone with a purchase order; because every watchmaker on earth has one on the bench; and because a replacement costs less than a service. The caliber reference found complete NH35A movements online for roughly $38 to $60, rising to $60 to $80 during the 2021 supply crunch, settling, and then "once again inflating due to tariffs" in its April 2025 update. NH34 GMTs sat at about $65 to $95.

That number matters more than any accuracy spec, because it is why our service cost guide concludes that on most watches this site recommends a scheduled overhaul is not worth paying for. When the whole engine is a $60 part, a watchmaker's honest advice at year eight is to swap it.

The flip side of that openness is counterfeiting. The caliber reference records that clones with sterile, unmarked rotors appeared first, and that outright fake NH35A movements now exist. This is a problem for people buying loose movements to mod a watch, not for someone buying a finished watch from a brand with a return policy - but it is one more reason to buy from the brand's own listing or an authorized seller rather than the cheapest storefront.

Which one is in your watch: the ten-second test

If the caseback is glass, read the rotor - unless the brand fitted a custom rotor, the caliber is engraved on it. If it is solid steel, the dial tells you most of it (day window means NH36, extra hand means NH34, 24-hour subdial means NH37 or NH39) and the crown tells you the rest:

• Crown in, turn clockwise. If you feel the mainspring winding, it is an NH3 or NH7 caliber. If the crown spins freely and does nothing, it is a 7S or NH25/26 - no hand winding.
• Crown out one click. Counterclockwise sets the date on all of them. Clockwise sets the day on an NH36, moves the GMT hand on an NH34, and does nothing on an NH35, NH37 or NH38.
• Crown out two clicks. The seconds hand should stop dead. If it keeps sweeping, you have a 7S26 or NH25 - working exactly as designed, not faulty.

That last step is worth doing on any watch whose seller could not name the caliber. The Invicta 8926 Pro Diver is the classic case: Invicta names no caliber on its listing, the caliber reference records the line carrying the NH25A and later the NH35A, and the watch has also shipped with the Miyota 8215 our review is written against - the display back is the only way to know which one you were sent. How to set an automatic watch walks the crown positions properly, including the hours in which you must not change the date.

Which watches we cover use one

• Seiko 5 Sports SRPD, SRPG31 field and the Turtle - the 4R36, so the day-date NH36 layout.
• Presage Cocktail Time and Prospex SRPF03 - the 4R35, date only, 23 jewels on the current B version.
• Seiko 5 Sports GMT and the SSK019/SSK003 pair - the 4R34, the GMT that became the NH34.
• Seiko SNK809 - the 7S26 ancestor. No hacking, no hand winding, 21 jewels, and now usually the worse buy against a 4R36 Seiko 5.
• Invicta Pro Diver 8926 - see above. The rotor decides.

The pattern is the same one the Miyota 8 series page describes from the other side: the movement industry is two Japanese suppliers selling to hundreds of brands, and the badge on the dial tells you less than the rotor does. Which supplier a brand chose is a fair proxy for what it was willing to spend - NH35 vs Miyota 8215 is the direct comparison.

Is it a good movement?

Yes, with the usual qualifier that it is a good cheap movement. In its favor: it hacks, it hand-winds, it winds in both directions, it has a published specification, it has fifteen years of production behind it and Seiko's own service network for the 4R version, and it is cheap enough to replace outright. Against it: the beat rate is the slow one, the accuracy band is wide, 41 hours is a day and a half, it is tall, and enthusiasts will point out that some components - the dial spacer among them - are plastic. None of that is a fault. All of it is why a $300 watch with one inside costs $300.

The honest comparison is Orient. Its in-house F6922 hacks, hand-winds, and carries a tighter published band of -15/+25 seconds a day at the same money, which is why the value picks on the under-$300 roundup are as often Orient as Seiko. Above $500 the Swiss 80-hour movements pull clearly away on reserve. Between those lines, an NH-powered watch is a perfectly sound thing to own - buy it for the case, the dial and the water rating, and treat the movement as a known quantity rather than a selling point. How to judge watch quality puts the movement in its proper place in that decision.