Not much else to say

 

Just FYI - to broaden your search, the balance used in the 503 is also used in the 490, 491, 500, 501, 502, 504, and 505.

 

Thanks

 

Part numbers from original parts list, later ones may be longer.

(ignore 1324, 1326 should get you out of trouble)



Or if your watchmaker just wants a balance staff.