Drop-in resolution
Ronda 5021.D vs Ronda 5040.B: do they swap?
Whether the Ronda 5021.D and Ronda 5040.B share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Ronda 5021.D (28.60 mm x 4.40 mm) and Ronda 5040.B (28.60 mm x 4.40 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 5021.D is a Swiss bicompax quartz chronograph, in two-register chronograph watches. The Ronda 5040.B is a full-feature Swiss quartz chronograph with a big date, in premium quartz chronographs.
They differ in calendar layout (bicompax chronograph, two sub-dials, date vs chronograph, small seconds, 1/10s, 30min and 10h counters, big date), winding behaviour. A two-register quartz chronograph at 28.60 mm x 4.40 mm. It shares the 5000-series family with the 5030.D but has a different sub-dial count, so a 5030.D dial will not fit it.
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.