Caliber reference
Seiko NH36 (TMI NH36A) caliber: dimensions and drop-in group
The published footprint of the Seiko NH36 (TMI NH36A) and which movements share it.
Used in: the day-date sibling of the NH35, adding a weekday disc on the same footprint.
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.
Drop-in group: Seiko NH3x / 4R day-date footprint (27.40 mm x 5.32 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.