Drop-in resolution
ETA 2804-2 vs Sellita SW215-1: do they swap?
Whether the ETA 2804-2 and Sellita SW215-1 share a case, and what changes if you move between them.
Interchangeable. The ETA 2804-2 and Sellita SW215-1 share the same 25.60 mm x 3.35 mm footprint and the same centre seconds, date at 3 layout, so one drops into the other's case with the correct dial and hands.
The ETA 2804-2 is the hand-wound date member of the 2800 family, the manual sibling of the 2824-2. The Sellita SW215-1 is the Sellita hand-wound with date, the drop-in alternative to the ETA 2804-2.
Their published figures are the same to the tenth of a millimetre. 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.