In addition, Quartzimotos Time Journal contains several excellent articles. Here is a link to the site:
http://quartzimodo.com/When it comes to Seiko’s entry level automatic movements, most people will readily think of the well-liked and reliable 7s-caliber automatics that are found in the garden variety SKX and limited edition SKZ divers and of course, the popular Seiko 5 family of affordable watches.
The 7s26 is perhaps the most widely known movement in the 7s-family and is extensively used in the base line Seiko 5 model. The Seiko 5 Sports and Seiko 5 Superiors are adorned with the slightly upmarket 7s36 movement, which has 23 jewels – two more jewels than what the 7s26 has. Limited production run 7s-caliber divers such as the SKZ203K Yellow
Monster and the SKZ201K Seiko 5 40th Anniversary diver’s watches also use the 7s36.
So what’s interesting about the 7s55?
The 7s55 appeared towards the later part of the 1990s and it was the shortest-lived member of the 7s family.
In essence, the 7s55 is mechanically similar to the date-only, 23-jeweled 7s35 caliber but fitted with a decorative “Tokyo Stripes” oscillating rotor with red inscription for aesthetic purposes. As with the other 7s family calibers, the 7s55 is a fully automatic movement, with no auxiliary hand winding or hacking feature and runs at the standard 21,600 beats per hour.
Unfortunately little is known about the history of the 7s55 movement as not many of them were made, compared to the mass produced 7s36. The bulk of 7s-caliber movements, prior to the end of 2006 were manufactured by the Seiko Instruments factory in, Singapore.
Above: Comparison of the 7s55 (left) with the plain looking 7s36 (right). Borrowed images.
The 7s55 was never used in any other Seiko model and it wouldn’t have made sense for a decorated movement like that to be used in a solid caseback diver’s watch, where it cannot be seen.
Models that used the 7s55 caliber The 7s55 debuted in a select range of Seiko 5 Superiors, which I call the “SLX-series” from their model reference numbers. All other Seiko 5 Superiors used the cheaper 7s36 day/date movement.
Only six variants were made: the SLX001K, 003K, 004K, 009K, 011K and 012K in stainless steel and gold tone guises with glass display backs to showcase its lovely rotor.
The SLX-series Superiors were cased at Seiko’s overseas production facility in Hong Kong while the movements were specially assembled in Japan. They were made available in small quantities to the Southeast Asian market. Contrary to what some have to be led to believe, these models were not exclusive to Japan although some Japanese collectors managed to get hold of the 7s55 Superiors.
The SLX-series Superiors were divided into two distinct designs: one with a subtle polygonal bezel edges, a date magnifier, Dauphin-styled hands, a larger crown and a plain stainless steel bracelet. The other design lacks a date magnifier but has a softly serrated bezel and baton-like hands. Both designs came in silver, black and silver dial with gold accents.
An unusual trait in the SLX Superiors is that they had regular bracelets which allows fitting of aftermarket leather straps. Seiko 5 Superiors made in 2003 onwards tended to have integrated bracelets, which I don’t really prefer.
The SLX-series Superiors were a hit with Seiko collectors and they were snapped up quickly. Due to its scarcity, the SLX Seiko 5 Superiors have earned its title as a collector’s item. A popular watch forum website in Thailand,
Siam Naliga succeeded in getting their Seiko to issue them with a customized, Siam Naliga official watch based on the black dialed SLX003K.
Made only to a mere 200 pieces and individually numbered, this limited edition SLX003K ensured a place in the Seiko Collectors’ Hall of Fame.
Will Seiko reintroduce the 7s55 in the future?
That would certainly be wishful thinking! Many years had passed since the 7s55 was discontinued and Seiko made no attempts to release additional models using this caliber. I don’t know why the Japanese watch company pulled out the 7s55 from production in a very short span of time, but I guess the movement was more expensive to make compared to the more common 7s26 and 7s36.
I doubt very much that Seiko will reintroduce the 7s55 caliber as they already have rolled out their recent 4R15 movement, which debuted in their
SRP-series mid-priced automatics in 2008.
There’s not much point in the 7s55 caliber making a comeback. For one thing, from the marketing perspective, the 4R caliber fits in between the flagship of the 7s-caliber family – the 7s36 and the more upmarket 6R15 movement, found in higher priced Seiko Premier, Spirit and Alpinist ranges.
For another, the reintroduction of the 7s55 movement would probably compete with Seiko’s 4R15 caliber. Seiko could have reissued the 7s55 long ago if they wanted to but they didn’t. I guess it wasn’t feasible for them to do so for marketing and cost reasons.
| Movement | Versions | Where assembled | Calendar | Beats/hour | Jewels | Models used |
| 7s26 | A, B | Singapore, Malaysia, Japan | Day/date | 21,600 | 21 | Seiko 5, SKX divers, |
| 7s25 | A | Japan | Date | 21,600 | 21 | SBDA-series Ti Samurai divers |
| 7s36 | A, B | Singapore, Malaysia, Japan | Day/date | 21,600 | 23 | Seiko 5 Sports, Seiko 5 Superior, SKZ divers, JDM Monster divers |
| 7s35 | A | Singapore, Malaysia | Date | 21,600 | 23 | SNM-series automatics and divers |
| 7s55 | A | Japan | Date | 21,600 | 23 | SLX-series Seiko 5 Superiors |
Above: Table showing the entire 7s caliber family and its attributes
The movement table above summarizes the features of the 7s caliber family. The 7s26 and 7s36 continues to power the Seiko 5 family of watches and 7s-caliber divers today. The date-only 7s35 debuted with the SNM001K, Seiko’s first automatic dress watch that didn’t belong to the Seiko 5 family. It is also used in the SNM-series divers such as the stainless steel Samurai divers and the North American “Landmonster” 200m divers.
Oddly enough, Seiko opted for the 7s25 instead of the 7s35 for its highly regarded but discontinued Ti Samurais. The 7s25 was not fitted to other models other than the SBDA-series Samurai divers. At the time of writing, it’s not known whether Seiko will reuse the 7s25 in their future models.
Subject: The little known Seiko 7s55 caliber 
Thu Feb 11, 2010 2:45 pm
back to my point; even the NH25A doesn't hand wind.
More great info Mark..Thx !