Drop-in resolution
Seiko 4R34 vs Seiko NH72 (TMI NH72A): do they swap?
Whether the Seiko 4R34 and Seiko NH72 (TMI NH72A) share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Seiko 4R34 (27.40 mm x 5.32 mm) and Seiko NH72 (TMI NH72A) (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 4R34 is the branded Seiko caller-GMT automatic, the retail version of the NH34. The Seiko NH72 (TMI NH72A) is the hacking, hand-winding skeleton member of the NH3x family.
They differ in calendar layout (centre seconds, GMT 24h hand, date at 3 vs full skeleton, no date, hacking). The branded Seiko GMT at 27.40 mm x 5.32 mm that the NH34 copies, with a 24-hour hand and date at 3. It shares the NH3x footprint and stem, so it interchanges with the NH34 within a GMT dial.
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.