Caliber reference
Sellita SW260-1 caliber: dimensions and drop-in group
The published footprint of the Sellita SW260-1 and which movements share it.
Used in: the automatic small-seconds caliber, in field and pilot watches with a sub-seconds dial at 6.
An automatic 11 1/2 ligne movement with small seconds at 6 and date at 3, at 25.60 mm x 5.60 mm. Its sibling SW290-1 moves the sub-seconds to 9, so the two are not interchangeable without a matching dial.
Drop-in group: 11 1/2 ligne automatic small seconds at 6 (25.60 mm x 5.60 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.