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You are here: Home / Families / Seiko 7S Family

Seiko 7S Family

Last Update: June 12, 2019

BRANDS: Seiko, Seiko Instruments Inc., Time Module Inc.

Production: 1996 – Current
1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s 2010s 2020s
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The Seiko 7S family was a widely-produced automatic watch movement produced from 1996 to the present. The NH family is also produced by Seiko Instruments (SII) but sold by Time Module (TMI) to third-party watch makers. The 7S family was the basis for the following 4R and 6R families.

The Seiko 7S was developed for reliability, economy, and ease of maintenance. It features a simplified design to reduce component count and cost, and some components are made of plastic to reduce the need for lubrication. Although it lacks hacking and hand-winding, it has bi-directional automatic winding thanks to the Seiko Magic Lever system. It oscillates at 21,600 A/h and returns respectable accuracy, though Seiko did not often specify the exact number. 7S movements were available in both 21- and 23-jewel versions, were revised many times (resulting in “A”, “B”, and even “C” variants), and were produced in factories in Singapore, Malaysia, and Japan.

The “B” series movements, introduced in October 2006, feature a new balance staff with open-ended stud carriers. The “C” series of about 2011 was more substantially revised, with over a dozen parts changes incompatible with previous movements.

The date-only 7S25 (and similar 7S35 and 7S55) are considerably rarer than the day-date 7S26 (and similar 7S36). Some date-only or time-only watches in fact use the day-date movement because it is so much more common, and the entire family is sometimes referred to as “7S26” due to its ubiquity.

TMI produced 7S movements as the NH25 and NH26 for third-party watch manufacturers. These were based on the updated 21-jewel 7S25B and 7S26B.

SII Cal. NH25 is the OEM equivalent of Seiko Cal. 7S25
21 Jewel23 Jewel
Date Only7S25A
7S25B
7S25C
NH25A
7S35A
7S35B
7S35C
7S55A
7S55B
Day-Date7S26A
7S26B
7S26C
NH26A
7S36A
7S36B
7S36C

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Calibre Start Year End Year Jewels Diameter (mm) Height (mm) Complications
Seiko 7S25 2004 2014 21 27.40 5.32 Date, Quick Date Correction
Seiko 7S26 1996 Current 21 27.40 4.90 Date, Day, Quick Date Correction, Quick Day Correction
Seiko 7S35 2003 2012 23 27.40 4.90 Date, Quick Date Correction
Seiko 7S36 1996 Current 23 27.40 4.90 Date, Day, Quick Date Correction, Quick Day Correction

Seiko 7S25

Seiko 7S26

Seiko 7S35

Seiko 7S36

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