Drop-in resolution
Sellita SW210-1 vs Miyota 8215: do they swap?
Whether the Sellita SW210-1 and Miyota 8215 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 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 SW210-1 is the Sellita hand-wound, the drop-in alternative to the ETA 2801-2. 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 (3.35 mm vs 5.67 mm), beat rate (28,800 A/h (4 Hz) vs 21,600 A/h (3 Hz)), 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.