Movement Caliber 431

431 Caliber
Gruen Caliber 431 Movement
Family: Veri-Thin
Base Movement: 430
Some parts interchangeable with:
Size (lignes):  8 3/4 "' x 9 3/4 "'
Jewels: 15
Year Introduced 1940
Mainspring Size in mm
1.18 x .105 x 247 
Mainspring Interchangeability
430 431 435 440 335
Fingerprint
(Movement Shape and Keyless works parts)
430 movement fingerprint
Page in Repairer's Reference: 
 
Style Numbers Used Per Year
431 Caliber Style Numbers Used
 
Marking variants

Notes
Is the 15 Jewel non-Precision version of the 430 family of Veri-Thins consisting of 430, 431, 435. 440 shares many of the same parts.