Drop-in resolution
Sellita SW210-1 vs Miyota 9015: do they swap?
Whether the Sellita SW210-1 and Miyota 9015 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Sellita SW210-1 (25.60 mm x 3.35 mm) and Miyota 9015 (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 SW210-1 is the Sellita hand-wound, the drop-in alternative to the ETA 2801-2. The Miyota 9015 is the slim premium Japanese automatic, a lower-cost slim alternative to the 2892 platform.
They differ in diameter (25.60 mm vs 26.00 mm), height (3.35 mm vs 3.90 mm), calendar layout (centre seconds, no date vs centre seconds, date at 3), winding behaviour. Sellita's hand-wound 11 1/2 ligne caliber at 25.60 mm x 3.35 mm, dimensionally matched to the ETA 2801-2. It is the direct manual-wind donor when a 2801-2 is unavailable.
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.