Drop-in resolution
Miyota 8215 vs Miyota 90S5: do they swap?
Whether the Miyota 8215 and Miyota 90S5 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Miyota 8215 (26.00 mm x 5.67 mm) and Miyota 90S5 (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 8215 is the low-cost Japanese workhorse, common in entry-level and fashion automatics. The Miyota 90S5 is the open-heart member of the 90 series, showing the balance through the dial.
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, date at 3 vs open heart, no date), winding behaviour. Close to the Swiss 11 1/2 core in diameter (26.00 mm) but taller at 5.67 mm and with a different dial-foot pattern, so it is not a drop-in for an ETA 2824 dial. Its seconds hand also has a soft, non-hacking stutter that is characteristic of the caliber.
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.