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Seiko 6306A

Probable

The JDM sibling of the 6309: 21 jewels against 17, hacking seconds where the 6309 has none, and a Kanji/English day wheel. It is the better movement, and the difference is real rather than a marketing distinction.

Specifications

Movement manufacturer
Seiko
Production
1976–1982
Frequency
21,600 vph (3 Hz)
Jewels
21
Winding
automatic
Complications
Day-date · Hacking seconds

Architecture

Automatic day-date diver's caliber with hacking seconds, supplied to the Japanese domestic market.

Authentication notes

  • MovementHigh confidence

    Hacking separates this caliber from the 6309 without opening the case

    Pull the crown to the setting position: the 6306A stops the seconds hand and the 6309A does not. Because the 6306-cased watch carries a substantial premium over the 6309, this thirty-second check is the single most valuable one on a Turtle, and it cannot be defeated by swapping a caseback.

Related calibers

  • Related caliber

    Seiko 6309A

    Export equivalent, without hacking and with four fewer jewels.

References using this caliber

Provenance of this record

Sources & Evidence

Primary sourceTechnical documentation

Seiko caliber technical guides and parts catalogues

Seiko Watch Corporation / Seiko Instruments

Accessed
2026-08-18

Cited for

This referenceHigh confidence
Secondary sourceSpecialist publication

Worn & Wound — Seiko diver and Daini Seikosha deep dives

Worn & Wound

Accessed
2026-08-18

Cited for

This referenceProbable
View source ↗

Last verified: Not yet reviewed