Drop-in resolution
Miyota 8205 vs Miyota 9015: do they swap?
Whether the Miyota 8205 and Miyota 9015 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Miyota 8205 (26.00 mm x 5.67 mm) and Miyota 9015 (26.00 mm x 3.90 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 8205 is the day-date member of the 8200 family, with a weekday disc alongside the date. The Miyota 9015 is the slim premium Japanese automatic, a lower-cost slim alternative to the 2892 platform.
They differ in height (5.67 mm vs 3.90 mm), beat rate (21,600 A/h (3 Hz) vs 28,800 A/h (4 Hz)), calendar layout (centre seconds, day and date at 3 vs centre seconds, date at 3), winding behaviour. Shares the 8215 footprint at 26.00 mm x 5.67 mm but adds a day disc at 3, so it needs a dial with day and date windows. It swaps with an 8215 case only if the dial carries the extra window.
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.