Drop-in resolution
Seiko NH38 (TMI NH38A) vs Seiko 7S36: do they swap?
Whether the Seiko NH38 (TMI NH38A) and Seiko 7S36 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Seiko NH38 (TMI NH38A) (27.40 mm x 5.32 mm) and Seiko 7S36 (27.40 mm x 5.60 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 NH38 (TMI NH38A) is the open-heart, no-date member of the NH3x family, in skeleton-dial mod watches. The Seiko 7S36 is the extra-jewel sibling of the 7S26, in many Seiko 5 sports models.
They differ in height (5.32 mm vs 5.60 mm), calendar layout (centre seconds, open heart, no date vs centre seconds, day and date at 3), winding behaviour. The open-heart, no-date member of the NH3x family at 27.40 mm x 5.32 mm, sharing the NH35 footprint and stem. It drops into an NH35 case but needs a dial with an open-heart aperture and no date window.
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.