Seiko Cal. 6640 - 991

The 6640-991 is a sought-after Hand-Winding piece from Seiko's golden era. Powered by the 6640 caliber with 29j jewels beating at 21,600 bph, it delivers a 51 hours power reserve. [seikata-wm-b58e5083f8b4]

Also known as: Sumo, Tuna

Specifications

Movement

Hand-Winding

Case Material

PVD Black

Case Width

42mm

Case Thickness

11.9mm

Lug Width

18mm

Crystal

Hardlex

Bezel

Inner Rotating

Water Resistance

60m

Dial Color

Silver

Jewels

29j

Frequency

21,600 bph

Power Reserve

51 hours

Year

1971

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