Drop-in resolution
Sellita SW300-1 vs ETA 2801-2: do they swap?
Whether the Sellita SW300-1 and ETA 2801-2 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Sellita SW300-1 (25.60 mm x 3.60 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 Sellita SW300-1 is the Sellita slim automatic, the drop-in alternative to the ETA 2892-A2. The ETA 2801-2 is the hand-wound, time-only member of the 2800 family, in slim dress watches.
They differ in height (3.60 mm vs 3.35 mm), calendar layout (centre seconds, date at 3 vs centre seconds, no date), winding behaviour. Dimensionally matched to the 2892-A2 at 25.60 mm x 3.60 mm, with four more jewels (25 vs 21). A current-production barrel lifts the reserve to 56 h without changing the caliber name or footprint.
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.