S. Epson Corp. Caliber Y120G Watch Movement

Seiko Epson Caliber Y120g

Manufacturer	S. Epson Corp. (Seiko/Hattori)
Caliber Number	Y120, Y120G
Type	Quartz
Lignes	6 3/4”’ x 8”’
Diameter	15.30mm x 18.2mm
Casing Diameter	15.30mm x 17.8mm
Height	2.99mm thick
Total Height	4.24mm to the top of the second hand pinio
Jewels	0
Battery Cell Number	377 (SR626SW) 1.55V
Battery Life	Estimated 4 years
Frequency	32,768 Hz
Quartz Type	Tuning fork type quartz crystal
Accuracy	+/- 20 seconds per month
Stem	0354788 or 0354787
Hand Sizes	1.10mm / .65mm
Functions	Central hours, central minutes
Country of Manufacture	Japan
Known Watches	(Too many to list, please add your watch in the comments below…)

The S. Epson Corp. caliber Y120 (aka Y120G) is a small size two-handed quartz watch movement with 0 jewels. It is made in Japan. Official documentation on this caliber has date stamps as recent as 2/28/18.

This movement is referred to as a ladies movement because of its small size, but it is also found in mens watches. There is also a long stem version of this movement available for large case watches which place the movement off center.

The movement pictured here also has a hexagon shape with the number 4 inside. The meaning of this marking is still unconfirmed, but it could be a reference to the factory it was produced in. If you know anything about this, please comment below.

Some of the topics covered in this caliber listing:

Variations A, B, C, D, E, F, etc:

You may see the caliber Y120 with different letters on the end. The letters indicate evolution versions of the caliber. As each letter advances, there may be slight changes made. They are all based on the same Y121 caliber and should work interchangeably. As of the latest tech sheets dated 11/30/18, the letter variation is G (Y120G).

Note: This movement is small, therefore the identifying markings are also small. For that reason, this caliber is sometimes incorrectly written as Y120Q. The G looks like a Q in some angles. It may also be written as Y12O which is also incorrect.

Accuracy:

S. Epson officially claims that the accuracy of this movement is +/- 20 seconds per month, while worn on the wrist in normal operating conditions and temperatures. The operating temperature range is -5 C to 50 C.

Technical Drawings:

Seiko Epson Caliber Y120g Drawings

Stem Removal:

The word “PUSH” with an arrow right facing is etched on the movement near the stem. The arrow is pointing to the stem release mechanism. It is a metal tab with a small indentation or dimple. Gently press that with your tool (tweezers, peg wood, or even a toothpick) and pull the stem out. Do not push too hard.

Replacement Price:

At the time of this post, replacement prices for the Y120G were found online for about $2.92 to $9.99 USD.

Examples of watches with this movement:

Seiko Epson Caliber Y120g Movement

The movement pictured in this caliber listing was found in a cheap $19.99 plastic NEFF watch. The picture above is what it looks like with the plastic movement holder.