Drop-in resolution
ETA 2804-2 vs Miyota 9015: do they swap?
Whether the ETA 2804-2 and Miyota 9015 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The ETA 2804-2 (25.60 mm x 3.35 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 ETA 2804-2 is the hand-wound date member of the 2800 family, the manual sibling of the 2824-2. The Miyota 9015 is the slim premium Japanese automatic, a lower-cost slim alternative to the 2892 platform.
They differ in diameter (25.60 mm vs 26.00 mm), height (3.35 mm vs 3.90 mm), winding behaviour. The manual-wind, date-at-3 version of the 2800 family at 25.60 mm x 3.35 mm. It adds a date disc to the 2801-2, so it needs a dial with a date window and swaps with the Sellita SW215-1.
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.