If You Do not Know Your Apple Watch Model Number ,So You Can Find Model Number Through A Few Steps

Identify your Apple Watch

Look up your Apple Watch model, collection, and color.

Find your model number

To learn which Apple Watch you have, use its model number:

1. Open the Apple Watch app on your iPhone. 
2. Tap the My Watch tab, then tap General > About.
3. Find the Model field. You should see the part number that begins with "M."  
4. Tap the Model field. You should see the field update to show a five-digit number that begins with "A." This is your model number. 
5. Compare your model number to the ones Click Here 

In Japan, if you have an Apple Watch Series 2 and the part number ends with "J/A," you can use Apple Pay on your device to ride transit and make purchases in stores.