Sellita SW510 caliber: dimensions and drop-in group

Used in: the tricompax Sellita chronograph, a 7750-family alternative with a 3-6-9 layout.

A 7750-family automatic chronograph at 30.00 mm x 7.90 mm, but arranged 3-6-9 rather than 6-9-12, with a longer 56 to 62 h reserve. The different subdial layout means it needs its own dial, not a 7750 dial.

Drop-in group: 7750-family chronograph, 3-6-9 (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.