ETA Valjoux 7750 caliber: dimensions and drop-in group

Used in: the reference Swiss automatic chronograph, in a large share of mechanical chronographs.

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.

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.