Drop-in resolution
Seiko NH36 (TMI NH36A) vs Seiko 4R36: do they swap?
Whether the Seiko NH36 (TMI NH36A) and Seiko 4R36 share a case, and what changes if you move between them.
Interchangeable. The Seiko NH36 (TMI NH36A) and Seiko 4R36 share the same 27.40 mm x 5.32 mm footprint and the same centre seconds, day and date at 3 layout, so one drops into the other's case with the correct dial and hands.
The Seiko NH36 (TMI NH36A) is the day-date sibling of the NH35, adding a weekday disc on the same footprint. The Seiko 4R36 is the branded day-date Seiko automatic, the retail version of the NH36.
Their published figures are the same to the tenth of a millimetre. Shares the NH35's 27.40 mm x 5.32 mm footprint and stem, so it drops into an NH35 case. The only change is the added day disc, which needs a dial with a day window and correct printing. It is the unbranded 4R36.
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.