Sellita SW300-1 caliber: dimensions and drop-in group

Used in: the Sellita slim automatic, the drop-in alternative to the ETA 2892-A2.

Dimensionally matched to the 2892-A2 at 25.60 mm x 3.60 mm, with four more jewels (25 vs 21). A current-production barrel lifts the reserve to 56 h without changing the caliber name or footprint.

Drop-in group: 11 1/2 ligne slim automatic (25.60 mm x 3.60 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.