|Caliber Number||5Y66, 5Y66A|
||1 piece stepping motor|
||351177 (tap 10)|
|Functions||Central hours; central minutes; central seconds; pointer date subdial at 3:00; 24 hour indicator at 6:00; retrograde day of the week between 8:00 and 11:00 (around 9:30)|
|Country of Manufacture||Japan (assembled)|
||(Add your watch to the comments below…)|
The Seiko caliber 5Y66 is a quartz day-date movement with no jewels.
The A in 5Y66A:
Your movement may be marked as a 5Y66A. The A indicates the evolution of the movement, with A being the first. Therefore 5Y66 is the same as 5Y66A. As of this post, only 5Y66A exists, not 5Y66B, C, etc.
5Y66 VS 5Y67:
There is a similar Seiko caliber 5Y67. They both share the same instructions manual and technical documentation. The main difference between the two movements is that the 5Y66 has a larger retrograde day of the week at 9:30 (between 8 and 11), and the 5Y67 has a retrograde day of the week at 10:30 (between 9:30 and 11:30).