Drop-in resolution
Sellita SW200-1 vs Seiko NH35 (TMI NH35A): do they swap?
Whether the Sellita SW200-1 and Seiko NH35 (TMI NH35A) share a case, and what changes if you move between them.
Different footprints. The Sellita SW200-1 is 25.60 mm x 4.60 mm and the Seiko NH35 (TMI NH35A) is 27.40 mm x 5.32 mm, so they do not share a case. This is a choice between platforms, not a swap.
The Sellita SW200-1 is the primary Swiss alternative to the 2824-2, now the default in many microbrands. The Seiko NH35 (TMI NH35A) is the default modding and microbrand automatic, hacking and hand-winding at low cost.
They differ in diameter (25.60 mm vs 27.40 mm), height (4.60 mm vs 5.32 mm), beat rate (28,800 A/h (4 Hz) vs 21,600 A/h (3 Hz)), winding behaviour. Matches the 2824-2 to the tenth of a millimetre in diameter and height, with the same date-at-3 layout, so it is the standard drop-in donor when a 2824-2 is unavailable. It carries one extra jewel (26 vs 25).
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.