Drop-in resolution
Sellita SW500 vs Sellita SW510: do they swap?
Whether the Sellita SW500 and Sellita SW510 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Sellita SW500 (30.00 mm x 7.90 mm) and Sellita SW510 (30.00 mm x 7.90 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 SW500 is the Sellita automatic chronograph, the drop-in alternative to the Valjoux 7750. The Sellita SW510 is the tricompax Sellita chronograph, a 7750-family alternative with a 3-6-9 layout.
They differ in calendar layout (chronograph, subdials at 6-9-12, day and date at 3 vs chronograph, subdials at 3-6-9, date). Built to the 7750 footprint at 30.00 mm x 7.90 mm with the same 6-9-12 subdial spacing, so it is the standard donor when a 7750 is unavailable. Subdial and calendar positions match, so 7750 dials and hands generally carry over.
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.