ETA 2660 caliber: dimensions and drop-in group

Used in: a small automatic without date, in compact ladies and slim cases.

A small no-date automatic at 17.20 mm x 4.80 mm, sharing the 2671's diameter but with no calendar. It is its own small footprint, not a drop-in for the 11 1/2 ligne core.

Drop-in group: 8 3/4 ligne small automatic, no date (17.20 mm x 4.80 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.