Drop-in resolution
ETA 2824-2 vs ETA 2801-2: do they swap?
Whether the ETA 2824-2 and ETA 2801-2 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The ETA 2824-2 (25.60 mm x 4.60 mm) and ETA 2801-2 (25.60 mm x 3.35 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 2824-2 is the reference Swiss workhorse automatic, used across mid-range Swiss brands for decades. The ETA 2801-2 is the hand-wound, time-only member of the 2800 family, in slim dress watches.
They differ in height (4.60 mm vs 3.35 mm), calendar layout (centre seconds, date at 3 vs centre seconds, no date), winding behaviour. The dimensional benchmark for the whole 11 1/2 ligne core. Any donor claiming 2824 compatibility is measured against 25.60 mm x 4.60 mm with date at 3.
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.