Seiko Instruments · Seiko NH35 / NH36

Invicta Pro Diver, microbrand divers and SKX mods: inside the Seiko NH35

The Seiko NH35 powers the Invicta Pro Diver, dozens of microbrand watches and many SKX mods. From a full wind it runs about 41 hours, or 1.7 days.

Updated September 2026 · Based on manufacturer specs, published reviews and watchmaker/owner reports

Watches that use the Seiko NH35

The NH35 is the automatic Seiko Instruments sells to other brands, so you won't see "Seiko" on the dial of most watches that use it. It's the default choice for affordable divers, field watches and microbrand designs, and its day-date twin, the NH36, is the go-to replacement for modders rebuilding a Seiko SKX. Seiko's own watches use the same design under the name 4R35 and 4R36, so they're listed here too.

The NH35 is date-only. The NH36 adds a day of the week. Everything else, including the 41-hour reserve, is the same.

Specs at a glance

History and where it came from

Seiko has two watch businesses. Seiko Watch Corporation makes Seiko-branded watches, and Seiko Instruments (SII, which sells movements through its TMI arm) makes movements for everyone else. The NH35A arrived in the early 2010s alongside Seiko's own 4R35, which appeared around 2011. The two are the same design. Only the rotor markings and the brand buying them differ.

Its predecessor, the NH25, was essentially the unbranded version of the Seiko 7S26 from the SKX007 and SNK809. It had no hacking and no hand-winding. The NH35 added both, which are the two features buyers of cheap automatics missed most. Combined with a very low price and a huge supply of parts, that made it the standard automatic for microbrands, fashion brands and larger budget makers like Invicta.

Accuracy in the real world

SII's specification is -20 to +40 seconds a day, measured on the bench within an hour of a full wind. Its technical guide also allows up to 60 seconds a day of difference between positions. That's a pass/fail band, not a target, and it's wide because the NH35 isn't finely adjusted in multiple positions at the factory. Monochrome notes the upper limit is 10 seconds more than the maximum for a standard-grade ETA.

Most examples do much better. Owners and watch sites commonly report single-digit or low double-digit daily rates once the watch has settled in, and plenty land within 10 seconds a day. Results vary with how the watch sits overnight. Crown up versus dial up can move the rate by several seconds. It also gets less consistent in the last quarter of its reserve, like most 3 Hz movements.

The good news is that it regulates easily. A watchmaker can bring a healthy NH35 much closer to zero in minutes, and hobbyists with a timegrapher often do it themselves.

Reliability and servicing

The NH35 has a strong reputation for toughness. It uses Seiko's Diashock protection and the simple Magic Lever winding system, which has been in use for decades. Many run for years without attention.

The economics of servicing it are unusual. As Time+Tide puts it, a new NH movement can cost around half the price of a service. A full strip-down, clean and oil at an independent often costs more than swapping in a fresh movement, so many watchmakers simply replace it. That's a feature, not a flaw: an Invicta or microbrand watch shouldn't need to be thrown away because the movement is tired.

The flip side is that an NH35 watch is rarely worth sending back to the brand. For most owners, a local watchmaker and a new movement is the sensible route.

Quirks worth knowing

• Rotor noise and wobble. The rotor spins freely and you can hear or feel it whirr on the wrist. A little play at the rotor's edge is normal for this design.
• Hand-winding takes a while. Winding by the crown feels gritty compared with Swiss movements, and SII's technical guide says it takes at least 55 turns to wind the mainspring fully from empty.
• Hacking isn't instant. The seconds hand stops when you pull the crown to the time position, but some examples keep moving for a beat or two.
• Date quickset in the danger zone. Don't quickset the date between roughly 9pm and 3am. Here's why.
• NH36 day-setting. On a day-date NH36, the first crown position turns one way for the date and the other way for the day.
• Magnetism. A sudden gain of minutes a day usually means it's magnetised. Demagnetising is quick and cheap.

How it compares

• Seiko 4R35 / 4R36: the same movement with Seiko on the rotor. Seiko quotes a slightly wider accuracy band (+45 to -35 s/day), but the parts and the 41-hour reserve are the same.
• Seiko NH34: the same base with a 24-hour GMT hand, used in the Seiko 5 Sports GMT and many microbrand GMTs.
• Seiko 7S26: the older movement in the original SKX007. It's just as tough, but it doesn't hack or hand-wind, which is why modders replace it with an NH35 or NH36.
• Miyota 8215: the closest rival on price. It's similarly durable, but it doesn't hack and its rotor is noisier.
• Miyota 9015: thinner, beats at 4 Hz for a smoother sweep, and costs more.
• Powermatic 80: nearly double the reserve at 80 hours, but costs more to buy and to fix.

Living with the 41-hour reserve

Forty-one hours is short by modern standards. Take your Invicta Pro Diver off after work on Friday and it will usually have stopped by Sunday morning. Leave a microbrand diver on the dresser all weekend and you'll be resetting the time and date on Monday, while avoiding the evening date-change window.

It also charges slowly on quiet desk days. A watch that only saw a few hours of gentle wear may not be full when you take it off, so the real figure is often shorter than 41 hours. If you rotate between several watches, the NH35 piece is usually the first to stop. Watch Winder counts down the reserve for each watch you own and reminds you before it stops, so you can wear it or give it a few dozen turns of the crown in time. For a one-off check, try the "Will my watch stop?" calculator.

Verdict

The NH35 isn't refined, and its spec sheet undersells how well most examples run. What it offers is tough, cheap-to-fix timekeeping with hacking and hand-winding, in almost any style of watch you can think of. That's why it's in everything from an Invicta Pro Diver to a carefully designed microbrand diver. Its one real weakness is the short reserve, and that's easy to manage once you know about it.

FAQ

How long does an Invicta Pro Diver run off the wrist?

An automatic Invicta Pro Diver with the NH35 runs about 41 hours from a full wind. Taken off Friday evening, it will usually stop some time on Sunday.

Does the Invicta 8926OB hack and hand-wind?

Yes. The NH35 in the 8926OB stops the seconds hand when you pull the crown to set the time, and it can be wound by turning the crown clockwise in its normal position.

Can you put an NH35 or NH36 in a Seiko SKX007?

Yes, it's one of the most common Seiko mods. It gives the SKX hacking and hand-winding, which the original 7S26 lacks. The NH36 keeps the day-date display.

How accurate is the Seiko NH35?

Seiko Instruments rates it at -20 to +40 seconds a day. Most examples run well inside that, often within about 10 seconds a day, and a watchmaker can regulate it closer.

Is the NH35 the same as the movement in the Seiko 5 Sports?

Essentially yes. The Seiko 5 Sports uses the 4R36, the Seiko-branded twin of the NH36, which is the NH35 with a day display added. The reserve is the same 41 hours.

What's the difference between the NH35 and the NH36?

The NH36 adds a day-of-week display next to the date. Size, accuracy and the 41-hour reserve are otherwise the same.

Should I service or replace an NH35?

Replacing is often cheaper. A new movement can cost less than a full service, so many watchmakers swap it rather than overhaul it.

Sources

• Time Module (SII): Cal. NH3 series technical guide
• Time+Tide: Why the Seiko NH35 is used by the best microbrands
• Monochrome: Alternatives to Swiss ETA and Sellita movements
• Caliber Corner: Seiko Caliber 4R35
• Chronometer Check: Seiko NH35/NH35a movement guide

Keeping it running

• On an average day an automatic gains roughly 4 hours of reserve per hour on the wrist, so about 10 hours of wear fills the Seiko NH35 / NH36. Desk days charge more slowly.
• Most automatics can also be wound by the crown. If yours has stopped, a few dozen turns gets it going before you put it on.
• Off the wrist it stops about 41 hours after it was last full. Stopped sooner?
• On a watch winder, start at about 650 turns per day, both directions. Winder settings for every movement.
• If it does stop, don't set the date between 9pm and 3am. Check if it's safe.

All Seiko movements

Never let it stop

Watch Winder counts down the reserve of every watch you own and reminds you before one stops. It already knows the Seiko NH35 / NH36: type your watch's name and the reserve fills itself in.

Manufacturer's published figure. Real reserve varies with the watch's age and service; check your manual.