Drop-in resolution
Miyota 9039 vs Miyota 90S5: do they swap?
Whether the Miyota 9039 and Miyota 90S5 share a case, and what changes if you move between them.
Same footprint, different calendar. The Miyota 9039 and Miyota 90S5 share the 26.00 mm x 3.90 mm case fit, but the Miyota 9039 is centre seconds, no date and the Miyota 90S5 is open heart, no date, so a swap needs a dial cut for the new layout.
The Miyota 9039 is the no-date member of the 90 series, popular in clean-dial microbrand watches. The Miyota 90S5 is the open-heart member of the 90 series, showing the balance through the dial.
They differ in calendar layout (centre seconds, no date vs open heart, no date). The no-date sibling of the 9015 at 26.00 mm x 3.90 mm, sharing the same dial-foot location. It drops into a 9015 case as long as the dial has no date window, which is its whole point.
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.