MovementSwap

Different footprints. The Miyota 8205 is 26.00 mm x 5.67 mm and the Seiko NH34 (TMI NH34A) is 27.40 mm x 5.32 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

Miyota 8205 vs Seiko NH34 (TMI NH34A): do they swap?

Whether the Miyota 8205 and Seiko NH34 (TMI NH34A) share a case, and what changes if you move between them.

No drop-in

Different footprints. The Miyota 8205 is 26.00 mm x 5.67 mm and the Seiko NH34 (TMI NH34A) is 27.40 mm x 5.32 mm, so they do not share a case. This is a choice between platforms, not a swap.

The Miyota 8205 is the day-date member of the 8200 family, with a weekday disc alongside the date. The Seiko NH34 (TMI NH34A) is the affordable modding GMT automatic, adding a caller-GMT hand to the NH35 base.

They differ in diameter (26.00 mm vs 27.40 mm), height (5.67 mm vs 5.32 mm), calendar layout (centre seconds, day and date at 3 vs centre seconds, GMT 24h hand, date at 3), winding behaviour. Shares the 8215 footprint at 26.00 mm x 5.67 mm but adds a day disc at 3, so it needs a dial with day and date windows. It swaps with an 8215 case only if the dial carries the extra 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.

Calibers and lookups

Miyota 820526.00 mm x 5.67 mm
Seiko NH34 (TMI NH34A)27.40 mm x 5.32 mm
Donor movement for Miyota 8205drop-in lookup
Donor movement for Seiko NH34 (TMI NH34A)drop-in lookup

Questions and answers

Miyota 8205 vs Seiko NH34 (TMI NH34A): do they swap?

Different footprints. The Miyota 8205 is 26.00 mm x 5.67 mm and the Seiko NH34 (TMI NH34A) is 27.40 mm x 5.32 mm, so they do not share a case. This is a choice between platforms, not a swap.