Seiko (SII) Caliber NH05A

The Seiko/TMI/SII/Epson caliber NH05A is a hand-windable and hacking automatic movement. At only 17.5mm diameter it is a fairly small movement and ideal for ladies size watches.

NH05A VS NH05B:

The trailing letters on Seiko calibers refer to the evolution of the caliber. There may be more differences than what are listed here, but after digging through all of the parts lists, it appears that the main differences between the A and B variants are:

Rotor:

The country of origin on the rotor (see below). NH05A lists Japan and Malaysia and the NH05B lists Japan, Malaysia, China.

Datewheel:

The datewheel. The NH05A datewheel is part number 0801-423 (they called it a “date dial”) and is described as being silver in color (plain metal) with black numbers printed on it. The NH05B datewheel (now referred to as a “date indicator”) is part number 0878-425, and is described as being a white background with black numbers. This may be that the material was possibly changed from metal to plastic as found in other NH models.

NH05 VS NH06:

There is a similar caliber NH06 with the same measurements and other specs, with the main difference being that the NH05 has a date and the NH06 has a day-date.

Accuracy:

Time Module documentation claims an accuracy rating of -35 ~ +55 seconds per day in normal operating temperatures.

Power Reserve:

Although the official documentation for the NH05 states a power reserve of “more than 40 hours”, microbrand E.C. Anderson claims this movement to have a 50 hour power reserve. If you have a watch with this movement, please comment below with your PR experience.

The mainspring of this caliber is fully wound after 55 turns of the crown. You cannot overwind this movement.

Country of Origin:

The NH05 is one of the only (if not the only) automatic movement from Seiko/TMI that is officially documented as being made in either Japan, Malaysia, or China. While Caliber Corner has suspected some movements are made in China, just from the sheer amount of movements sold from China-based sellers (and the fakes now coming from there).

This admission shows that Seiko has moved some mechanical movement production to China. Could the future of NH movements be “made in China”? We shall see – or maybe there’s nothing to see since SII/TMI has been making it part of their practice to not mark the country of origin on their movements – see pics of an actual movement above and below!

Interestingly, the arrival of a China labeled rotor has only shown up on the NH05B tech sheets (dated November 16, 2022). The NH05A documentation (dated April 15, 2009) only pictures a Japan or Malaysia options. Therefore, sometime between the NH05A and NH05B, production was added in China.

Beware of watch brands and watch parts sellers claiming they are providing a Japanese or made in Japan movement, then shipping you a movement with no country of origin markings. Japan is proud country and Seiko is proud to be made in Japan – when a movement is made in Japan, Seiko is sure to write JAPAN on it. Disagree? Please provide a written statement from Seiko Instruments stating that made in Japan calibers are not signed “Japan”. Few NH05 movements are being made in Japan. Just because Seiko is a Japan based company does not make the NH05 a made in Japan movement? Want to argue this point? Feel free to contact US customs to discuss. Might as well call the FTC while you’re at it.

Crown/Stem Removal:

The NH05 is a tiny calibre, making it a bit more challenging to navigate around the architecture of the movement. With the crown and stem to the right, there will be a small hole with a button just above it near the edge of the movement. This is the setting lever axle, creating a detent button which will put opposing pressure on the setting lever, allowing for extraction of the stem. The “button” is very small and will require fine tip tweezers or other tool to fit properly.

Here is what it looks like from the dial side:

Replacement Prices:

At the time of this post, caliber NH05 replacement prices were found online for around $69.29.

Watches with this caliber:

E.C. Andersson:

One microbrand watch using this movement is E.C. Andersson’s North Sea II. It appears that they went with the NH05 to get the effect of a centrally positioned date wheel.

This is what is posted on their site about it:

“E.C. Andersson uses the SEIKO NH05, a movement that is beloved around the world. Known to be extremely reliable, thanks to the solid built. The SEIKO NH05 often outlives many of its competitors by far, and are easy to service.” –source

There is an interesting thread that the brand started on WUS where they mention an issue with the NH05 having a stuttering seconds hand:

“During manufacturing, we found an odd characteristic of the movement. Since we love the abilities of the NH05, we decided to do some digging. . . . The NH05 is built like a tank, however, we found that when hand-wound or put under great shock, the seconds-hand would “hiccup” for a while before settling into its normal pace. We ran all possible tests, reassembled the watches, and individually regulated all movements, reaching a level of accuracy that was beyond our ambitions and counterable to far more expensive brands. We managed to manufacture a fantastic solid metal movement holder and new, sturdier dial-clamps. Striving to be quick to action, we also made the obvious move to remove the seconds-hand and launch the watch as a two-hander, which arguably harmonizes better with the watch’s overall look. . . . We couldn’t just let the seconds hand mystery go unsolved however and decided to do some research. The occasional “hiccups” indicated a seemingly unsolvable trait of the movement, yet we remained curious and overwrought to modify the NH05’s behavior. By tightening the tubes of the central stem plus all hands, and eventually manufacturing a new seconds hand of aluminum, it turned out much to our joy, the charming yet curious seconds-hand “coughing” had been cured. We are very proud to say that the seconds-hand equipped North Sea ref NS01FD was successfully sold even before finishing the North Sea II.”

CIGA Design:

Another microbrand using the NH05 is CIGA Design in their Series U Black Hole watch. Using such a small movement in this model made sense for the design which features a sort of floating dial with coming out from the sides, curved upwards to give the effect of being sucked into a black hole. Their site only states that it is an NH05, not whether it’s an NH05A or NH05B. The brand is based in China and refers to the movement as “Original Japanese Seiko NH05 movement”. The movement images on their site do not appear to have a country of origin stamp.

If you know any other watches with this movement, add it to the comments section below…

Additional Images:

The NH05A example featured on this page were found in this 40mm E.C. Andersson North Sea II discussed above. Here you can see the large movement holder that was mentioned.

Additional Images:

• Official tech guide and drawings (pdf)
• Official NH05 instruction manual (pdf)
• NH05B parts list (pdf)
• List of Seiko movements