MovementSwap

Different footprints. The Miyota 8205 is 26.00 mm x 5.67 mm and the Seiko 6R15 is 27.40 mm x 5.25 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 6R15: do they swap?

Whether the Miyota 8205 and Seiko 6R15 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 6R15 is 27.40 mm x 5.25 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 6R15 is the predecessor of the 6R35, a date automatic in earlier Prospex and Presage models.

They differ in diameter (26.00 mm vs 27.40 mm), height (5.67 mm vs 5.25 mm), calendar layout (centre seconds, day and date at 3 vs centre seconds, 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 6R1527.40 mm x 5.25 mm
Donor movement for Miyota 8205drop-in lookup
Donor movement for Seiko 6R15drop-in lookup

Questions and answers

Miyota 8205 vs Seiko 6R15: do they swap?

Different footprints. The Miyota 8205 is 26.00 mm x 5.67 mm and the Seiko 6R15 is 27.40 mm x 5.25 mm, so they do not share a case. This is a choice between platforms, not a swap.