Drop-in resolution
Ronda 6203.B vs Ronda 505: do they swap?
Whether the Ronda 6203.B and Ronda 505 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Ronda 6203.B (26.00 mm x 3.30 mm) and Ronda 505 (25.60 mm x 3.10 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 6203.B is a Swiss quartz caliber with a second time zone display in GMT-style watches. The Ronda 505 is a three-hand Swiss quartz caliber in the 500 family, at the 11 1/2 ligne size.
They differ in diameter (26.00 mm vs 25.60 mm), height (3.30 mm vs 3.10 mm), calendar layout (dual time and date at 3 vs centre seconds, date at 3, small seconds sub-variant), winding behaviour. A quartz movement at 26.00 mm x 3.30 mm carrying a dual-time (second time zone) function alongside the date. Its extra 24h train means it needs a matching multi-hand dial and is not a plain three-hand swap.
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.