Drop-in resolution
Seiko VD53 (SII) vs Ronda 505: do they swap?
Whether the Seiko VD53 (SII) and Ronda 505 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Seiko VD53 (SII) (25.60 mm x 3.20 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 Seiko VD53 (SII) is a three-hand quartz caliber with tall hands, in analogue quartz 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 height (3.20 mm vs 3.10 mm), calendar layout (centre seconds, date at 3, high hands vs centre seconds, date at 3, small seconds sub-variant), winding behaviour. A three-hand date quartz caliber at 25.60 mm x 3.20 mm sharing the 11 1/2 ligne diameter. Like all quartz calibers it is not a mechanical donor, and it competes with the Ronda 515 and ETA 955.112 at the same diameter.
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.