MovementSwap

Different footprints. The Seiko NH36 (TMI NH36A) is 27.40 mm x 5.32 mm and the Miyota 8218 is 26.00 mm x 5.67 mm, so they do not share a case. This is a choice between platforms, not a swap. Published dimensions, layout and the checks before you swap one for the other.

Updated 05 September 2026.

Drop-in resolution

Seiko NH36 (TMI NH36A) vs Miyota 8218: do they swap?

Whether the Seiko NH36 (TMI NH36A) and Miyota 8218 share a case, and what changes if you move between them.

No drop-in

Different footprints. The Seiko NH36 (TMI NH36A) is 27.40 mm x 5.32 mm and the Miyota 8218 is 26.00 mm x 5.67 mm, so they do not share a case. This is a choice between platforms, not a swap.

The Seiko NH36 (TMI NH36A) is the day-date sibling of the NH35, adding a weekday disc on the same footprint. The Miyota 8218 is a day-date 8200 member, in entry automatics that show the weekday.

They differ in diameter (27.40 mm vs 26.00 mm), height (5.32 mm vs 5.67 mm), winding behaviour. Shares the NH35's 27.40 mm x 5.32 mm footprint and stem, so it drops into an NH35 case. The only change is the added day disc, which needs a dial with a day window and correct printing. It is the unbranded 4R36.

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.

Calibers and lookups

Seiko NH36 (TMI NH36A)27.40 mm x 5.32 mm
Miyota 821826.00 mm x 5.67 mm
Donor movement for Seiko NH36 (TMI NH36A)drop-in lookup
Donor movement for Miyota 8218drop-in lookup

Questions and answers

Seiko NH36 (TMI NH36A) vs Miyota 8218: do they swap?

Different footprints. The Seiko NH36 (TMI NH36A) is 27.40 mm x 5.32 mm and the Miyota 8218 is 26.00 mm x 5.67 mm, so they do not share a case. This is a choice between platforms, not a swap.