Drop-in resolution
Ronda 515 vs Ronda 6203.B: do they swap?
Whether the Ronda 515 and Ronda 6203.B share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Ronda 515 (25.60 mm x 3.00 mm) and Ronda 6203.B (26.00 mm x 3.30 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 515 is a common Swiss three-hand quartz movement in mid-range quartz watches. The Ronda 6203.B is a Swiss quartz caliber with a second time zone display in GMT-style watches.
They differ in diameter (25.60 mm vs 26.00 mm), height (3.00 mm vs 3.30 mm), calendar layout (centre seconds, date at 3 vs dual time and date at 3), winding behaviour. A quartz caliber that shares the 25.60 mm 11 1/2 ligne diameter. It is not a mechanical donor: swapping a quartz Ronda for an automatic ETA changes power source, height and hand heights entirely. It swaps with the same-size Ronda 513S and 6203.B quartz calibers.
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.