> For the complete documentation index, see [llms.txt](https://docs.raidrobotics.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.raidrobotics.org/raidparts/designer-guide/build-the-bom.md).

# Build the BOM

The bill of materials lives in **Design › Bill of materials**, organized in three levels.

| Level       | What it is                                                             | Who sets it up      |
| ----------- | ---------------------------------------------------------------------- | ------------------- |
| Subsystem   | A section of the robot, like Drivetrain or Intake, with a 2-digit code | Admins, each season |
| Subassembly | A group of parts inside a subsystem, numbered 1 to 9 automatically     | Designers           |
| Design part | One part in a subassembly, with its part number assigned for you       | Designers           |

## Add parts

1. Open **Design › Bill of materials** and pick the subsystem (use **Subsystems** to switch).
2. Click **+ Assembly** to add a subassembly. It gets the next number in that subsystem.
3. Expand the subassembly and click **+ Part** to add each design part by name. The part number is assigned automatically.

![A subassembly expanded in the Bill of materials, with its review thread and design parts](https://2105095865-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FX3JOc9Z4ZYAoJCFFCn5v%2Fuploads%2Fgit-blob-f5e71d8463d8ad8b3a9854b6a21f32ef34f13782%2Fdesign-bom.jpg?alt=media)

## Read a part number

Design part numbers look like `26-01101`:

| `26`        | `01`           | `1`         | `01`           |
| ----------- | -------------- | ----------- | -------------- |
| Season year | Subsystem code | Subassembly | Part, 01 to 99 |

## Comments and activity

Every design part and subassembly has a comment thread: type in **Add a comment…** and click **Comment** (or press ⌘/Ctrl + Enter). Review steps, change requests, and obsolete or delete requests are recorded there with who did it and when, so the thread doubles as the part's history.

Next: [Review](/raidparts/designer-guide/review.md).


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