Drop-in resolution
Sellita SW215-1 vs Miyota 9039: do they swap?
Whether the Sellita SW215-1 and Miyota 9039 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Sellita SW215-1 (25.60 mm x 3.35 mm) and Miyota 9039 (26.00 mm x 3.90 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 SW215-1 is the Sellita hand-wound with date, the drop-in alternative to the ETA 2804-2. The Miyota 9039 is the no-date member of the 90 series, popular in clean-dial microbrand watches.
They differ in diameter (25.60 mm vs 26.00 mm), height (3.35 mm vs 3.90 mm), calendar layout (centre seconds, date at 3 vs centre seconds, no date), winding behaviour. The date-at-3 hand-wound member of the SW210 family at 25.60 mm x 3.35 mm, dimensionally matched to the ETA 2804-2. It is the direct manual-wind date donor.
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.