The Seiko 4N21-0990 is a watch model based on the 4N21 movement.
Parts List
| 170P17SN03 | crystal - crystal |
| 170P01SN03 | crystal - crystal |
| 6K40A5SNG0 | crown - crown |
| 0F175BAA1 | case back gasket |
| AC004BAA1 | case back gasket - crown and stem gasket |
| 86561171 | crystal gasket |
| D0P2AG | band - band |
| D0P4AG | band - band |
| 3BA075F1BNG | others - second hand |
| 1BB047A1BNG | others - hour hand |
| 2BB070A1BNG | others - minute hand |
| A120BS | others - push pin (for lb) |
| 4N212060XS14 | others - dial |
| 4N212070XL14 | others - dial |
| 4N2164 | others - machine code |
| 82833515 | others - case ring |
| 4N2109906YA | others - case |
| 4N210990 | others - case back |
| 4N2109906YB | others - case |
| 0351155 | others - winding stem |