Drop-in resolution
Seiko 4R35 vs Seiko NH70 (TMI NH70A): do they swap?
Whether the Seiko 4R35 and Seiko NH70 (TMI NH70A) share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Seiko 4R35 (27.40 mm x 5.32 mm) and Seiko NH70 (TMI NH70A) (27.40 mm x 5.32 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 4R35 is the branded Seiko date automatic behind many Presage and Prospex models. The Seiko NH70 (TMI NH70A) is the fully skeletonised member of the NH3x family, in open-worked mod watches.
They differ in calendar layout (centre seconds, date at 3 vs full skeleton, no date, no seconds hand), winding behaviour. The branded Seiko caliber that the NH35 copies, at 27.40 mm x 5.32 mm with date at 3. It shares the NH35 footprint and stem, so the two interchange within the 27.40 mm case.
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.