Caliber reference
Sellita SW500 caliber: dimensions and drop-in group
The published footprint of the Sellita SW500 and which movements share it.
Used in: the Sellita automatic chronograph, the drop-in alternative to the Valjoux 7750.
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.
Drop-in group: 7750 chronograph footprint, 6-9-12 (30.00 mm x 7.90 mm). 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.