Seiko NH35 (TMI NH35A) caliber: dimensions and drop-in group

Used in: the default modding and microbrand automatic, hacking and hand-winding at low cost.

Larger than the Swiss core at 27.40 mm, so it will not drop into a case cut for a 25.60 mm ETA. It is the unbranded version of the Seiko 4R35 and shares that caliber's footprint and stem.

Drop-in group: Seiko NH3x / 4R date footprint (27.40 mm x 5.32 mm, date at 3). 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.