The Seiko 4M21-0B20 is a watch model based on the 4M21 movement.
Parts List
| 270A20SB0C | crystal - crystal |
| 8M35A4SNGA | crown - crown |
| 0F260NA1S | case back gasket - case back gasket |
| 80607389 | pusher - button |
| D0S6CZ | band - band |
| 1BF080L0BCF | others - hour hand |
| 2BF115L0BCF | others - minute hand |
| 12ST08CG | others - second hand |
| 81400709 | others - button spring clip |
| EG0060B01 | others - button gasket |
| 0351552 | others - winding stem |
| 81190055 | others - bracelet fixing pipe |
| 81604959 | others - bracelet fixing pin |
| 82837180 | others - case ring |
| 4M210B20XB | others - case |
| 4M210B20 | others - case back |
| 4M210B40XN14 | others - dial |
| 4M211 | others - machine code |
| AD006BA12 | others - crown gasket |
Caliber 4M21
Other models with the same movement
| 4M21-0010 |
| 4M21-0A10 |
| 4M21-0A20 |
| 4M21-0A30 |
| 4M21-0A40 |
| 4M21-0A50 |
| 4M21-0A60 |
| 4M21-0A70 |
| 4M21-0A80 |
| 4M21-0A90 |
| 4M21-0B00 |
| 4M21-0B0A |
| 4M21-0B10 |
| 4M21-0B30 |
| 4M21-0B40 |
| 4M21-0B50 |
| 4M21-0B60 |
| 4M21-0B70 |
| 4M21-0B80 |
| 4M21-0B90 |
| 4M21-0C00 |
| 4M21-0C10 |