Seiko · Seiko 7S26

Seiko SKX007, SNK809 and Monster power reserve: inside the 7S26

The Seiko SKX007, SKX009, the original Monster and the Seiko 5 SNK809 all run on the 7S26. From a full wind it runs about 41 hours, or 1.7 days, and it can only be wound by wearing it.

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

Watches that use the Seiko 7S26

If you own a Seiko diver or Seiko 5 made between the late 1990s and the late 2010s, there's a good chance it has a 7S26 inside. It's the movement behind the SKX007, the watch that taught a generation of enthusiasts what a proper dive watch is, and behind the cheap, tough 37 mm Seiko 5s like the SNK809. The case back usually gives it away: SKX divers are marked 7S26-0020, 7S26-0030 and so on.

The Seiko 5 Sports SNZG, SNZH and SNZF look like they belong here, but they use the 23-jewel 7S36, which is the same movement with two extra jewels.

Specs at a glance

History and where it came from

Seiko introduced the 7S26 in 1996, the same year the SKX007 appeared. For more than 20 years it was the heart of Seiko's cheapest automatics: the SKX divers, the Monster and dozens of Seiko 5 models. For many watch enthusiasts, an SKX007 or SNK809 was the first mechanical watch they owned, and the 7S26 was the first movement they learned about.

It was built to a price. Leaving out hacking and hand-winding cut parts and cost, and Seiko's Magic Lever winding system keeps the automatic winding simple. Worn & Wound describes it as built around four primary moving parts, "one of the simplest automatic systems around". The result is a movement that is very hard to kill.

There were three versions. The original 7S26A was replaced by the 7S26B in 2006 and later by the 7S26C. Seiko's technical guide says the C uses new parts that don't interchange with the B, though complete movements are the same size and fit the same watches.

From around 2011 Seiko began moving its entry-level range to the 4R36, which adds the two missing features. The SKX007, SKX009 and SKX011 were discontinued in 2019 and replaced by the 4R36-powered Seiko 5 Sports SRPD range, which owners nicknamed the "5KX". See our Seiko 5 Sports review for the successor.

Accuracy in the real world

The figure you'll see most often for the 7S26 is -20 to +40 seconds a day. Seiko's current combined 7S/4R instruction manual lists the reserve, jewels and beat rate but no accuracy figure for the 7S26, so treat that tolerance as the widely quoted one rather than an official promise. Caliber Corner cites a looser +45/-35 from community reports.

Real examples usually do far better than the tolerance. Worn & Wound's review SKX007 ran about 4 seconds a day fast, and owners commonly report 5 to 20 seconds fast on a healthy one. The movement uses a conventional regulator (Seiko calls it the Etachron system), so a watchmaker can adjust the rate quickly.

Age is now the bigger factor. Most 7S26 watches on the used market are 7 to 30 years old, and many have never been serviced. Dried oils make a movement run fast, erratic, or stop early, and regulation won't fix that until it has been cleaned.

Setting the time to the second is fiddly because the seconds hand keeps running. The trick owners use is to pull the crown and turn the hands gently backward: on many examples this briefly holds the seconds hand. It's a workaround that puts light stress on the gear train, so don't lean on it.

Reliability and servicing

The 7S26's reputation for toughness is deserved. SKX007s have been worn swimming, diving, working and travelling for years without a service, and the simple layout gives it less to go wrong than a hand-winding, hacking movement.

• Service or swap. An independent watchmaker can service one easily. Because a complete replacement movement is cheap, many shops simply fit a new one.
• The NH36 route. The NH36 fits most SKX cases, bringing hacking and hand-winding. This is the basis of the huge SKX modding scene. Collectors who want an original SKX usually keep the 7S26.
• Parts. Seiko's technical guide notes the B and C versions use different parts, so a watchmaker needs to know which one is inside.

Quirks worth knowing

• Winding by motion only. Turning the crown does nothing to the mainspring. If it has stopped, Seiko's manual says to swing the watch from side to side for about 30 seconds, then wear it.
• No hacking. The seconds hand keeps running while you set the time.
• Day and date setting. In the first crown position, one direction advances the date and the other the day. Avoid setting either between about 9pm and 3am. Here's why.
• Rotor noise. The rotor spins freely in one direction, and you can hear and feel it when you move your wrist quickly. That's normal.
• Wind-up from stopped. A day of wear rarely fills a 7S26 from empty, especially at a desk. It may run short the first night.
• Magnetism. Seiko rates it to 4,800 A/m. A sudden big gain usually means it's magnetised, which a watchmaker fixes in seconds.

How it compares

• Seiko 7S36: the same movement with 23 jewels instead of 21, used in the Seiko 5 Sports SNZG and SNZH. No practical difference in daily use.
• Seiko 4R36 and NH36: the 7S26's successors, with the same 41-hour reserve and the hacking and hand-winding it lacks. The better movement to live with.
• Orient F6922: the 7S26's old rival in the Orient Kamasu and Mako. Similar size and accuracy, but it hacks and hand-winds.
• Seiko 6R15: Seiko's step-up movement of the same era, with 50 hours, hand-winding and a tighter tolerance.
• ETA 2824-2: the Swiss equivalent of the time. Faster 4 Hz beat, hacking and hand-winding, but more expensive to buy and service.

Living with the 41-hour reserve

Forty-one hours is short, and without hand-winding it shapes how you use the watch. Take your SKX007 off at 6pm on Friday and, if it was fully wound, it stops around lunchtime on Sunday. On Monday morning you have to shake it to life and set the time, day and date again. You can't top it up from the crown on Sunday night.

It's worse if the spring wasn't full. After a week of desk days an SKX or SNK809 may have far less than 41 hours stored, and it can stop overnight if you take it off at bedtime. If you rotate an SKX with other watches, the practical fix is to wear it for a few hours before it runs out rather than reset it.

That's where knowing the reserve helps. Watch Winder counts down the 41-hour reserve for each watch you own and reminds you before it stops, which matters more than usual on a watch you can't wind by hand. For a one-off check on a weekend, use the "Will my watch stop?" calculator.

Verdict

The 7S26 is simple, tough and easy to service, and it made the SKX007 and SNK809 legends at their price. Its limits are real: no hacking, no hand-winding, a short reserve and a loose tolerance. For a collector's SKX, keep it and service it; it will outlast most owners' interest. For a watch you want to wear daily and set precisely, the 4R36-powered Seiko 5 Sports or an NH36-swapped SKX is easier to live with.

FAQ

How long does a Seiko SKX007 run off the wrist?

A fully wound SKX007 runs about 41 hours, so it will usually stop on Sunday if you take it off on Friday evening. If it wasn't fully wound, it stops sooner.

Does the Seiko SKX007 hack or hand-wind?

No. The 7S26 in the SKX007 and SKX009 doesn't stop the seconds hand when you pull the crown, and turning the crown doesn't wind the mainspring. It winds only through wrist movement.

Why did my Seiko SKX stop overnight?

Most likely the mainspring wasn't full. Light wear or desk days may store much less than 41 hours, and you can't top it up by hand. Wear it more actively or swing it gently for a few minutes before taking it off.

How do I start a stopped Seiko SNK809?

Swing the watch gently from side to side for about 30 seconds until the seconds hand runs, then set the time and put it on. The crown won't wind it.

How accurate is the Seiko SKX007?

The commonly quoted tolerance for its 7S26 is -20 to +40 seconds a day. Healthy examples often run 5 to 20 seconds fast, and a watchmaker can regulate one closer.

What movement is in the Seiko Orange Monster?

The second-generation Orange Monster SKX781 and Black Monster SKX779 use the 7S26. Later Monster models moved to the 4R36, which hacks and hand-winds.

What is the difference between the 7S26 and 7S36?

The 7S36 has 23 jewels instead of 21, with the two extra jewels on the third and escape wheels. Otherwise they are the same movement with the same 41-hour reserve.

Can I put an NH36 in my SKX007?

Yes. The NH36 fits most SKX cases and adds hacking and hand-winding with the same reserve. It is the most common SKX modification.

Sources

• Seiko: Cal. 7S26C/7S36C parts list and technical guide
• Seiko: Cal. 4R15/4R16/4R35/4R36/7S26/7S35/7S36 instructions
• Caliber Corner: Seiko Caliber 7S26
• Worn & Wound: Seiko SKX007 review
• Strapcode: Seiko caliber 7S26 review

Watches we've reviewed with the Seiko 7S26

• Seiko 5 SNK809 and SNXS review (7S26)

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 7S26. 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 7S26: 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.