Drop-in resolution
Sellita SW216-1 vs Miyota 9075: do they swap?
Whether the Sellita SW216-1 and Miyota 9075 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Sellita SW216-1 (25.60 mm x 4.35 mm) and Miyota 9075 (26.00 mm x 4.92 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 SW216-1 is the hand-wound small-seconds caliber, in classic dress watches with a sub-seconds dial. The Miyota 9075 is the Miyota true-GMT (traveller) automatic, in affordable GMT travel watches.
They differ in diameter (25.60 mm vs 26.00 mm), height (4.35 mm vs 4.92 mm), calendar layout (small seconds at 6, date at 3 vs centre seconds, true GMT 24h hand, date at 3), winding behaviour. A hand-wound 11 1/2 ligne caliber with small seconds at 6 and date at 3, taller than the SW215-1 at 4.35 mm because of the separate seconds train. It needs a small-seconds dial and is not interchangeable with a centre-seconds movement.
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.