The Seiko 8420-6640 is a watch model based on the 8420 movement.
Parts List
| ES9N38SN00 | crystal |
| 25M04EE1 | crown |
| 0Z1800N01 | case back gasket |
| WI085 | others - other band |
| 06R23ZSH | others - hour hand |
| DZ0041B01 | others - crown and stem gasket |
Caliber 8420
Seiko 8420-6640 Watch Guide