ETA SA 3501

Caliber 3501 is a rectangular manual-winding mechanical movement manufactured by ETA SA in Switzerland. It operates at 28,800 vph with 18 jewels and features Kif shock protection. A distinctive characteristic is its mainspring lock mechanism, which prevents overwinding—a feature the user manual explicitly notes as unlike most handwound watches. ETA recommends service at least every four years to address aging of oils and grease in the movement.