Drop-in resolution
Sellita SW260-1 vs Miyota 8215: do they swap?
Whether the Sellita SW260-1 and Miyota 8215 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Sellita SW260-1 (25.60 mm x 5.60 mm) and Miyota 8215 (26.00 mm x 5.67 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 SW260-1 is the automatic small-seconds caliber, in field and pilot watches with a sub-seconds dial at 6. The Miyota 8215 is the low-cost Japanese workhorse, common in entry-level and fashion automatics.
They differ in diameter (25.60 mm vs 26.00 mm), height (5.60 mm vs 5.67 mm), beat rate (28,800 A/h (4 Hz) vs 21,600 A/h (3 Hz)), calendar layout (small seconds at 6, date at 3 vs centre seconds, date at 3), winding behaviour. An automatic 11 1/2 ligne movement with small seconds at 6 and date at 3, at 25.60 mm x 5.60 mm. Its sibling SW290-1 moves the sub-seconds to 9, so the two are not interchangeable without a matching dial.
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.