> ## Documentation Index
> Fetch the complete documentation index at: https://docs.firstresonance.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Overview

> How ION models a part: its identity, revisions, fields, tracking type, and link to physical inventory.

A part is a definition, not a physical object. The physical units that exist against it are [inventory](/manage-supply-chain/inventory), and one part can back many inventory records across locations, each a serial, a lot, or a plain quantity.

You curate the definition in the Parts Library and act on the physical units in Inventory. Bills of materials, procedures, runs, purchase orders, and issues all reference parts. To reach a part's on-hand stock, see [Search parts and reach inventory](/build-hardware/parts/inventory-search).

## Identity and revisions

A part number and its revision together identify a part. The same part number can repeat only under a different revision.

A revision captures an engineering change. Creating one makes a new part record linked to the old, so history stays intact: runs and BOMs already built against the earlier revision keep pointing to it, while new builds pick up the latest. You retire an old revision by archiving it once nothing in flight still needs it.

A revision scheme sets how revision values count up, such as `A`, `B`, `C`; `1`, `2`, `3`; or `00-1`, `00-2`. You define schemes once for the org and assign one to each part, and a new part starts at the scheme's first value. To move a part onto a different scheme, either cast it to carry the current revision into the new sequence, or reset it to start over at the new scheme's first value. For the steps, see [Set a part's revision scheme](/build-hardware/parts/revision-schemes).

## Fields

| Field                               | Notes                                                                                                                                |
| ----------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------ |
| **Part Number**                     | Org-unique within revision. Required.                                                                                                |
| **Revision**                        | Engineering revision value from the part's revision scheme. Read-only on the part page.                                              |
| **Description**                     | Free text.                                                                                                                           |
| **Revision Scheme**                 | Governs how this part's revision values increment. Required.                                                                         |
| **Tracking**                        | `LOT`, `SERIAL`, or `None`. See [Serial and lot tracking](/build-hardware/parts/serial-lot-tracking).                                |
| **Purchase Type**                   | `Creates inventory`, `Does Not Create Inventory, Physically Received`, or `Does Not Create Inventory, Digitally Received`. Required. |
| **Sourcing Strategy**               | `Make`, `Buy`, or `Dual source`. Drives MRP and procurement.                                                                         |
| **Cost**                            | Optional. Feeds BOM rollups and inventory valuation.                                                                                 |
| **Lead Time**                       | Optional. Drives reorder timing and Autoplan.                                                                                        |
| **Maintenance Interval**            | Optional. Shown only for `Tool` parts that need scheduled maintenance.                                                               |
| **Unit of Measurement**             | Optional. The unit the part is counted or measured in.                                                                               |
| **Reorder Point Minimum / Maximum** | Optional. Triggers reorder workflows when on-hand drops below the minimum.                                                           |
| **Image**                           | Optional. A thumbnail for visual identification.                                                                                     |

A part's status (**Released** or **Archived**) shows in the page header and changes with the **Archive** or **Release** action, not as a field. Supplier part numbers live in the **Suppliers** section of the part page; see [Manage parts](/build-hardware/parts/creating-managing).

<Tip>
  Your org can add **custom attributes** to parts for data the built-in fields don't cover. See [Custom attributes](/administration/custom-attributes).
</Tip>

## Tracking types

A part's tracking type, set in the **Tracking** field, decides how ION identifies and traces each unit:

* **Serial**: every unit gets a unique serial number.
* **Lot**: units move in batches under a shared lot number.
* **Untracked**: ION tracks only the count.

Tracking type reaches into receiving, inventory, installs, run history, issues, and traceability, and each type behaves differently across all of them. Set it before any inventory exists, because switching once stock is on hand is constrained. For the downstream differences, number generation, and switching rules, see [Serial and lot tracking](/build-hardware/parts/serial-lot-tracking).

## Lifecycle

A part is **Released** when you create it and **Archived** when it leaves production. ION never deletes a part, because runs, issues, BOMs, purchase orders, and inventory all point back to it. Archiving preserves that history and hides the part from active pickers, such as BOM and PO lines. You can release an archived part again at any time.