MovementSwap

Different footprints. The Miyota 8200 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 8200 vs Seiko NH34 (TMI NH34A): do they swap?

Whether the Miyota 8200 and Seiko NH34 (TMI NH34A) share a case, and what changes if you move between them.

No drop-in

Different footprints. The Miyota 8200 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 8200 is the no-date base of the 8200 family, in clean-dial entry automatics. 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, no date vs centre seconds, GMT 24h hand, date at 3), winding behaviour. The no-date base of the 8200 family at 26.00 mm x 5.67 mm, mechanically the 8215 without the date train. It shares the 8215 case footprint and drops into an 8200-series case cut for a no-date dial.

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 820026.00 mm x 5.67 mm
Seiko NH34 (TMI NH34A)27.40 mm x 5.32 mm
Donor movement for Miyota 8200drop-in lookup
Donor movement for Seiko NH34 (TMI NH34A)drop-in lookup

Questions and answers

Miyota 8200 vs Seiko NH34 (TMI NH34A): do they swap?

Different footprints. The Miyota 8200 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.