Drop-in resolution
Sellita SW220-1 vs Sellita SW210-1: do they swap?
Whether the Sellita SW220-1 and Sellita SW210-1 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Sellita SW220-1 (25.60 mm x 5.05 mm) and Sellita SW210-1 (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 SW220-1 is the Sellita day-date, the drop-in alternative to the ETA 2836-2. The Sellita SW210-1 is the Sellita hand-wound, the drop-in alternative to the ETA 2801-2.
They differ in height (5.05 mm vs 3.35 mm), calendar layout (centre seconds, day and date at 3 vs centre seconds, no date), winding behaviour. The day-date member of the SW200 family, dimensionally matched to the ETA 2836-2 including the 5.05 mm height and day-and-date-at-3 layout.
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.