Drop-in resolution
Ronda 513S vs Ronda 6004.B: do they swap?
Whether the Ronda 513S and Ronda 6004.B 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 Ronda 6004.B (25.60 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 513S is a three-hand no-date Swiss quartz movement at the 11 1/2 ligne size. The Ronda 6004.B is a long-battery-life Swiss quartz three-hander in mid-range watches.
They differ in height (3.00 mm vs 3.30 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.