Drop-in resolution
Seiko NH70 (TMI NH70A) vs Seiko 7S36: do they swap?
Whether the Seiko NH70 (TMI NH70A) and Seiko 7S36 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Seiko NH70 (TMI NH70A) (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 NH70 (TMI NH70A) is the fully skeletonised member of the NH3x family, in open-worked 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 (full skeleton, no date, no seconds hand vs centre seconds, day and date at 3), winding behaviour. A fully skeletonised NH3x caliber at 27.40 mm x 5.32 mm, sharing the family footprint and stem but designed to be seen through the dial. It needs a skeleton dial and has no seconds hand or date; the NH72 is its hacking, hand-winding sibling.
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.