MovementSwap

Close in diameter, not a drop-in. The Seiko 4R36 (27.40 mm x 5.32 mm) and Seiko 6R15 (27.40 mm x 5.25 mm) are near in size but differ in height, dial feet or layout, so moving between them means a new dial, hands and often a case adjustment. Published dimensions, layout and the checks before you swap one for the other.

Updated 05 September 2026.

Drop-in resolution

Seiko 4R36 vs Seiko 6R15: do they swap?

Whether the Seiko 4R36 and Seiko 6R15 share a case, and what changes if you move between them.

Adapter needed

Close in diameter, not a drop-in. The Seiko 4R36 (27.40 mm x 5.32 mm) and Seiko 6R15 (27.40 mm x 5.25 mm) are near in size but differ in height, dial feet or layout, so moving between them means a new dial, hands and often a case adjustment.

The Seiko 4R36 is the branded day-date Seiko automatic, the retail version of the NH36. The Seiko 6R15 is the predecessor of the 6R35, a date automatic in earlier Prospex and Presage models.

They differ in height (5.32 mm vs 5.25 mm), calendar layout (centre seconds, day and date at 3 vs centre seconds, date at 3). The branded day-date Seiko at 27.40 mm x 5.32 mm that the NH36 copies. It shares the NH3x footprint and stem, so it drops into an NH36 case with a matching day-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

Seiko 4R3627.40 mm x 5.32 mm
Seiko 6R1527.40 mm x 5.25 mm
Donor movement for Seiko 4R36drop-in lookup
Donor movement for Seiko 6R15drop-in lookup

Questions and answers

Seiko 4R36 vs Seiko 6R15: do they swap?

Close in diameter, not a drop-in. The Seiko 4R36 (27.40 mm x 5.32 mm) and Seiko 6R15 (27.40 mm x 5.25 mm) are near in size but differ in height, dial feet or layout, so moving between them means a new dial, hands and often a case adjustment.