Drop-in resolution
Seiko NH35 (TMI NH35A) vs Seiko 4R35: do they swap?
Whether the Seiko NH35 (TMI NH35A) and Seiko 4R35 share a case, and what changes if you move between them.
Interchangeable. The Seiko NH35 (TMI NH35A) and Seiko 4R35 share the same 27.40 mm x 5.32 mm footprint and the same centre seconds, date at 3 layout, so one drops into the other's case with the correct dial and hands.
The Seiko NH35 (TMI NH35A) is the default modding and microbrand automatic, hacking and hand-winding at low cost. The Seiko 4R35 is the branded Seiko date automatic behind many Presage and Prospex models.
Their published figures are the same to the tenth of a millimetre. Larger than the Swiss core at 27.40 mm, so it will not drop into a case cut for a 25.60 mm ETA. It is the unbranded version of the Seiko 4R35 and shares that caliber's footprint and stem.
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.