Sellita SW1000-1 caliber: dimensions and drop-in group

Used in: a small Sellita automatic with date, in compact and mid-size watches.

A small automatic with date at 20.00 mm x 3.90 mm. It shares the SW100-1 diameter but at a taller height, so the two are near but not drop-in twins, and neither fits the 11 1/2 ligne core.

Drop-in group: 8 3/4 ligne small automatic (20.00 mm x 3.90 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.