Drop-in resolution
Miyota OS20 vs Seiko VK64 (SII): do they swap?
Whether the Miyota OS20 and Seiko VK64 (SII) share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Miyota OS20 (30.80 mm x 5.10 mm) and Seiko VK64 (SII) (30.80 mm x 5.10 mm) are near in size but differ in height, dial feet or layout, so moving between them means a new dial, hands and often a case adjustment.
The Miyota OS20 is a common low-cost Japanese quartz chronograph module, in analogue quartz chronographs. The Seiko VK64 (SII) is the bicompax meca-quartz chronograph, in two-register chronograph mods.
They differ in calendar layout (chronograph, three sub-dials, date at 4:30 vs meca-quartz bicompax chronograph, two sub-dials, date), winding behaviour. A quartz chronograph at 30.80 mm x 5.10 mm with three sub-dials (24h at 3, small seconds at 6, minutes at 9) and a date at 4:30. It is a full-size chronograph module and needs a matching multi-subdial dial, not a plain three-hand swap.
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.