Caliber reference
Seiko VK63 (SII) caliber: dimensions and drop-in group
The published footprint of the Seiko VK63 (SII) and which movements share it.
Used in: the reference meca-quartz chronograph for modders, a quartz base with a mechanical chrono module.
A meca-quartz chronograph at 30.80 mm x 5.10 mm: quartz timekeeping with a snap-back mechanical chronograph. It has three sub-dials and a date; the VK64 is its bicompax relative with a different sub-dial count.
Drop-in group: Seiko VK meca-quartz chronograph, 3 sub-dials (30.80 mm x 5.10 mm). Matching diameter and height is necessary but not sufficient. A donor is only a true drop-in when the dial-foot positions, hand-hole sizes, stem length and calendar layout also match. Two movements can share a case and still need a new dial, re-broached hands or a cut-to-length stem.