When the Illinois Watch Company introduced their extra-thin 12-Size Model 3 around 1921, the movement had been refined to an impressive thickness of approximately 4.3mm with the dial installed.
This remarkable engineering represented a 30% reduction in the thickness compared to the standard 12-Size movements.
Measurements Compared (12s Extra-Thin Model 3 vs. 12s Standard Model 3):
Pillar Plate Diameter: 40.0mm vs. 39.7mm
Upper Plate Diameter: 36.6mm vs. 36.5mm
Thickness: 4.32mm vs. 6.15mm
Weight (Movement, Dial, Hands): 25.55g vs. 32.39g