Caliber reference
ETA / Unitas 6497-1 caliber: dimensions and drop-in group
The published footprint of the ETA / Unitas 6497-1 and which movements share it.
Used in: the large pocket-watch caliber used in oversized hand-wound wristwatches.
A large 16 1/2 ligne hand-wound movement at 36.60 mm x 4.50 mm with small seconds at 9. It shares its size with the 6498-1, which differs only by placing the small seconds at 6, so the two are footprint twins but need their own dials.
Drop-in group: 16 1/2 ligne hand-wound, small seconds at 9 (36.60 mm x 4.50 mm). 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.