Caliber reference
Seiko NH34 (TMI NH34A) caliber: dimensions and drop-in group
The published footprint of the Seiko NH34 (TMI NH34A) and which movements share it.
Used in: the affordable modding GMT automatic, adding a caller-GMT hand to the NH35 base.
The GMT member of the NH3x family at 27.40 mm x 5.32 mm, adding a 24-hour hand to the NH35's date layout. It shares the NH35 case footprint and stem, so it drops into an NH35 case but needs a GMT dial and hand set. It is the unbranded Seiko 4R34.
Drop-in group: Seiko NH34 / 4R34 GMT footprint (27.40 mm x 5.32 mm, GMT hand). 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.