Seiko Selection Open Heart HFB003J Automatic Cal. 4R38 – Black Dial 40mm Stainless Steel 100m Made in Japan

• Seiko-manufactured automatic caliber 4R38 with 24 jewels, manual winding, and hacking seconds.
• Open Heart dial design with an open window at 9 o’clock that allows you to view the balance wheel and escapement in continuous operation.
• Approximate power reserve of 41 hours with mechanical operation—no batteries required.
• Black dial with applied hour markers and faceted, polished hands that ensure a clean, high-contrast readout.
• Stainless steel case, 40 mm in diameter and 11.8 mm thick, with a combination of brushed and polished finishes.
• Reinforced Hardlex mineral crystal, resistant to everyday impacts and scratches.
• Water resistance of 100 meters (10 bar / 10 ATM), suitable for swimming and continuous exposure to water.
• Transparent screw-down case back showcasing the oscillating weight and components of the mechanical caliber.
• Stainless steel link bracelet with a folding clasp featuring safety pushers.
• Entirely manufactured in Japan (Made in Japan) and part of the exclusive Japanese domestic market (JDM) catalog.

The Seiko Selection HFB003J combines the timeless elegance of a three-hand mechanical watch with the visual dynamism of its Open Heart window at the 9 o’clock position. This opening reveals the beating heart of the movement, displaying the back-and-forth motion of the balance wheel and the escape wheel without needing to remove the watch from the wrist.

Inside, the 4R38 caliber powers the watch—an automatic movement designed by the Japanese manufacturer to ensure long-term reliability. It features manual winding via the crown and a seconds-stop function for precise time synchronization, and omits the date display to maintain a clean, symmetrical dial.

With a 40-mm-diameter case and a slim profile of 11.8 mm, this model stands out for its water resistance of 10 bar (100 m), offering greater robustness than is typical for dress watches. The design is completed by a see-through crystal case back and a solid stainless steel bracelet with side release pushers.

Detailed Specifications
Brand / Collection Seiko / Seiko Selection (JDM)
Reference HFB003J
Movement Automatic with manual winding (Seiko Caliber 4R38)
Power Reserve Approx. 41 hours
Frequency / Jewels 21,600 vibrations/hour (3 Hz), 24 jewels
Country of Origin Japan (Made in Japan)
Functions Hours, minutes, seconds, seconds stop, open-heart movement
Case Material Stainless steel
Case Diameter 40.0 mm
Case Thickness 11.8 mm
Crystal Hardlex
Case Back: Screw-down transparent case back
Dial Color: Black with open heart at 9 o’clock
Bracelet: Stainless steel with push-button folding clasp
Water Resistance: 100 m / 10 bar (10 ATM)
Anti-magnetic Protection: JIS Class 1 (4,800 A/m)