Seagull ST3620 (Unitas 6498)

The Sea-Gull ST3620 is a manual-wind mechanical watch movement and an unlicenced clone of the famous Swiss ETA Unitas 6498 caliber. [1, 2, 3]

It is widely used by hobbyist watchmakers, custom builders, and microbrands. [1, 2]

Watch a breakdown and comparison of the Sea-Gull ST3600 and ST3620 movements:

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Key Specifications

• Type: Manual-wind (hand-wound) mechanical movement
• Swiss Equivalent: ETA / Unitas 6498 (small seconds sub-dial at the 6 o'clock position)
• Jewels: 17 jewels
• Vibration / Beat Rate: 21,600 vibrations per hour (vph) or 3 Hz
• Power Reserve: Approximately 48 hours
• Dimensions: Roughly 36.6 mm diameter (though pocket-watch and case implementations can vary) [1, 2, 3, 4, 5, 6]

Design and Layout

• Seconds Sub-Dial: The ST3620 features the small seconds hand positioned at 6 o'clock. (Its sister movement, the ST3600, mirrors the ETA 6497 with the seconds hand at 9 o'clock). [1, 2]
• Architecture: Based on a large pocket-watch caliber design, making it relatively large, easy to handle, and popular for use in pilot-style or oversized wristwatches. [1, 2]

Common Characteristics & Quirks

• Affordability & Modding: Popular for custom builds, skeleton variants (such as the ST36K), and learning watchmaking because parts and replacement movements are inexpensive. [1, 2, 3]
• Tolerances and QC: As a clone, its factory quality control, tolerances, and finishing can vary compared to Swiss originals. Some builders note minor fitting differences or ridges depending on the case design. [1, 2]
• Winding Pinion Nuance: Some watchmakers note a known design quirk where the stock winding pinion can occasionally skip or slip against the crown wheel compared to a genuine ETA part, though it remains functional

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The ST 3621variation

The Sea-Gull ST3621 (also known as TY3621) is a mechanical hand-winding watch movement made by Tianjin Seagull in China. It is a clone and variant of the classic Swiss ETA/Unitas 6498 pocket watch movement. [1]

Specifications

Type: Mechanical hand-winding (manual-wind) [1]
Diameter: 37.2 mm [1]
Height/Thickness: 4.5 mm [1]
Jewels: 17 jewels [1]
Beat Rate: 21,600 vph (3 Hz) [1]
Power Reserve: Approximately 45 hours [1]
Functions: Central hours and minutes, with a small seconds sub-dial positioned at 6 o'clock [1]
Shock Protection: Incabloc-style anti-shock system [1]
Hacking: No hacking (seconds hand does not stop when pulling out the crown) [1]

Key Differences from ST3600

Small Seconds Position: The ST3621 features the small seconds sub-dial at the 6 o'clock position (savonette or hunter style configuration), whereas the sibling ST3600 places the small seconds at 9 o'clock (lepine style configuration). [1]

Common Uses & Characteristics

Watch Styles: Because of its large pocket-watch size (37.2 mm), it is commonly used in large vintage-style pilot (Flieger) watches, trench watches, and affordable mechanical dress watches (such as models from Lobinni, Geervo, and Hruodland).
Winding Experience: Users on Reddit generally agree that the manual-wind operation of the large movement provides an engaging and tactile winding experience reminiscent of vintage timepieces.

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