Drop-in resolution
ETA 2671 vs Sellita SW100-1: do they swap?
Whether the ETA 2671 and Sellita SW100-1 share a case, and what changes if you move between them.
Interchangeable. The ETA 2671 and Sellita SW100-1 share the same 17.20 mm x 4.80 mm footprint and the same centre seconds, date at 3 layout, so one drops into the other's case with the correct dial and hands.
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The ETA 2671 is the small ladies automatic, in compact and slim cases with a date. The Sellita SW100-1 is the Sellita small automatic with date, sized like the ETA 2671.
Their published figures are the same to the tenth of a millimetre. A miniaturised automatic at 17.20 mm x 4.80 mm, effectively a shrunken 2824. It shares nothing dimensionally with the 11 1/2 ligne core: it is its own small footprint, paired only with the slightly larger 2681.
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.