Drop-in resolution
Ronda 513S vs ETA 955.112: do they swap?
Whether the Ronda 513S and ETA 955.112 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Ronda 513S (25.60 mm x 3.00 mm) and ETA 955.112 (25.60 mm x 3.15 mm) are near in size but differ in height, dial feet or layout, so moving between them means a new dial, hands and often a case adjustment.
The Ronda 513S is a three-hand no-date Swiss quartz movement at the 11 1/2 ligne size. The ETA 955.112 is a common Swiss three-hand quartz caliber, the ETA rival to the Ronda 515.
They differ in height (3.00 mm vs 3.15 mm), calendar layout (centre seconds, no date vs centre seconds, date at 3), winding behaviour. The no-date three-hand member of the Ronda 500 quartz family at 25.60 mm x 3.00 mm. It shares the 515 footprint and stem, differing only by the absence of a date, so the two swap within a matching dial.
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.