Drop-in resolution
ETA 2801-2 vs Miyota 82S5: do they swap?
Whether the ETA 2801-2 and Miyota 82S5 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The ETA 2801-2 (25.60 mm x 3.35 mm) and Miyota 82S5 (26.00 mm x 5.67 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 2801-2 is the hand-wound, time-only member of the 2800 family, in slim dress watches. The Miyota 82S5 is the small-seconds open-heart 8200 member, in decorated entry automatics.
They differ in diameter (25.60 mm vs 26.00 mm), height (3.35 mm vs 5.67 mm), beat rate (28,800 A/h (4 Hz) vs 21,600 A/h (3 Hz)), calendar layout (centre seconds, no date vs small seconds, open heart, no date), winding behaviour. The manual, no-date base of the 2800 family at 25.60 mm x 3.35 mm. It shares the family diameter but has no rotor and no calendar, so it swaps only with the Sellita SW210-1 hand-wound 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.