Drop-in resolution
ETA Valjoux 7750 vs Sellita SW500: do they swap?
Whether the ETA Valjoux 7750 and Sellita SW500 share a case, and what changes if you move between them.
Interchangeable. The ETA Valjoux 7750 and Sellita SW500 share the same 30.00 mm x 7.90 mm footprint and the same chronograph, subdials at 6-9-12, day and date at 3 layout, so one drops into the other's case with the correct dial and hands.
The ETA Valjoux 7750 is the reference Swiss automatic chronograph, in a large share of mechanical chronographs. The Sellita SW500 is the Sellita automatic chronograph, the drop-in alternative to the Valjoux 7750.
Their published figures are the same to the tenth of a millimetre. A larger 13 1/4 ligne movement at 30.00 mm x 7.90 mm with the classic 6-9-12 subdial layout. Its drop-in donors are the Sellita SW500 and SW510, which copy its dimensions and subdial positions.
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.