Drop-in resolution
Ronda 5030.D vs Ronda 5021.D: do they swap?
Whether the Ronda 5030.D and Ronda 5021.D share a case, and what changes if you move between them.
Different footprints. The Ronda 5030.D is 28.00 mm x 4.40 mm and the Ronda 5021.D is 28.60 mm x 4.40 mm, so they do not share a case. This is a choice between platforms, not a swap.
The Ronda 5030.D is the reference Swiss quartz chronograph, in a large share of quartz chronographs. The Ronda 5021.D is a Swiss bicompax quartz chronograph, in two-register chronograph watches.
They differ in diameter (28.00 mm vs 28.60 mm), calendar layout (chronograph, small seconds at 3, 12h at 6, 30min at 9, date at 4 vs bicompax chronograph, two sub-dials, date), winding behaviour. A quartz chronograph at 28.00 mm x 4.40 mm with sub-dials at 3, 6 and 9 and date at 4. It is the go-to quartz chrono module; the smaller 5021.D is its bicompax relative, not a drop-in.
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.