Japanese original YN55A YN56A precision automatic mechanical movements

The Epson YN55 and YN56 (often labeled as YN55A / YN56A) are Japanese automatic, mechanical watch movements manufactured by Seiko Epson. If they look familiar, it’s because they are the unbranded/supply market equivalents of Orient’s in-house F6 calibers (the F6722 and F6922) which famously power watches like the Orient Mako and Ray lines. Epson sells these YN movements to third-party microbrands (such as San Martin, Vostok Europe, and Guanqin) as an alternative to the incredibly ubiquitous Seiko Instruments (SII) NH35/NH36 series. YN55: Features a Single Calendar (Date only at 3:00). YN56: Features a Double Calendar (Day & Date). Compared to the NH35 series, watchmakers and microbrands often note that the YN series features tighter modern manufacturing tolerances out of the factory, resulting in very stable positional variance. However, note that while the hour and minute hands from an NH35 fit the YN55/YN56, the seconds hand hole size is slightly different and dial feet layout follows a template closer to the Miyota 8215. Specification List Specification Epson YN55A (Single Calendar) Epson YN56A (Double Calendar) Manufacturer Seiko Epson Seiko Epson Movement Type Automatic (Self-Winding) & Manual Winding Automatic (Self-Winding) & Manual Winding Base Caliber Clone Orient Cal. F6722 Orient Cal. F6922 Functions Hours, Minutes, Central Seconds, Date Hours, Minutes, Central Seconds, Day, Date Jewels 22 22 Vibrations Per Hour 21,600 bph (3 Hz) 21,600 bph (3 Hz) Power Reserve $\ge$ 40 hours $\ge$ 40 hours Hacking? (Stop Seconds) Yes Yes Factory Accuracy -25 to +35 seconds per day -25 to +35 seconds per day Lift Angle 52° 52° Shock System Seiko Diashock Seiko Diashock Diameter 27.4 mm 27.4 mm Casing Diameter 29.36 mm (with spacer) 29.36 mm (with spacer) Height (Thickness) 5.32 mm 5.32 mm Hand Sizes (H/M/S) 1.50mm / 0.90mm / 0.20mm 1.50mm / 0.90mm / 0.20mm Country of Manufacture Japan Japan