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Seiko Sii Caliber Vk64a Mecaquartz

SII Hattori Caliber VK64A

Seiko Sii Caliber Vk64a Mecaquartz

Manufacturer Seiko Instruments Inc. / SII / Hattori / TMI
Caliber Number VK64, VK64A
Type Quartz (mecaquartz)
Diameter 13 1/2”’ (30.80mm x 29.10mm)
Casing Diameter
Height 5.10mm
Battery Cell Number 394 (SR936SW)
Frequency Unknown (please comment below)
Quartz Type Tuning fork type quartz crystal
Stem 351177/tap 10 or 351892/tap 11
Hand Sizes 1.50/.90/.32mm
Functions Hours, minutes, central chronograph seconds, 1/5 seconds, 60 minute counter at 9:00, 24 hour indicator at 3:00, date at 6:00
Country of Manufacture Japan (assembled)
Known Models AVI-8 Flyboy, EMG Horizon Chrono (list yours in the comments below…)

The Seiko Instruments (SII) caliber VK64A is part of the hybrid mechanical quartz (mecaquartz) movement line. It is a chronograph movement that uses quartz technology for the main functions of the watch, and a mechanical module for operating the chronograph. Learn more here.

Seiko Sii Caliber Vk64a

Accuracy Rating:

Seiko/Time Module states that the expected accuracy of this movement is less than +/- 20 seconds per month at normal temps. The battery life is about 3 years with normal operation.

Sweeping Chronograph Seconds:

As a mecaquartz type of movement, the chronograph second hand on the VK64 has a rather smooth sweeping motion, unlike most quartz chronographs that impulse with a ticking motion.

Battery Replacement:

After installing a fresh battery cell, remember to reset the circuit by touching the AC terminal of the circuit block (look for an arrow labeled AC pointing to a hole) and the switch spring with your tweezers.

Replacement Prices:

At the time of this post, replacement prices for this movement were found online in the range of $17.95 to $34.95.


The Seiko labeled caliber number for the VK64 is 6T64. You might find this caliber VK64 listed as being produced by SII aka Hattori aka TMI (Time Module Inc) aka Seiko Instruments Inc. Learn more about the different names here. Other calibers with the same base movement are VK61, VK63, VK67, VK68, VK73, and VK83.

Examples of watches with caliber VK64:

The watch below is an AVI-8 Flyboy with a VK64A inside.

Seiko Sii Caliber Vk64a Wide

Additional Resources: