# Order subscription items

Order subscription items can be of type `skus`, `bundles`, or `adjustments` and are used to generate the target order's line items involved in the automatic [order subscriptions](/core-api-reference/order_subscriptions.md) generation using [recurring order copies](/core-api-reference/recurring_order_copies.md). Order subscription items are automatically generated from the source order's line items with frequency, according to the strategy set at the [subscription model](/core-api-reference/subscription_models.md) level:

* `by_frequency` — for each automatically generated order subscription as many order subscription items as the source order’s line items that have that specific frequency will be generated.
* `by_line_items` — for each automatically generated order subscription one order subscription item only will be generated.

Like line items, order subscription items have a `quantity` and a unit price — both inherited from the source order's line items — that can be changed anytime by updating the order subscription item itself to customize the generated target order's line items. If the source order's line items unit price is computed according to a [price frequency tier](/core-api-reference/price_frequency_tiers.md), any change to the tier itself that happens after the order subscription item generation won't be reflected on the order subscription item unit price.

<details>

<summary>Data model</summary>

Check the related [ER diagram](/data-model/orders/subscriptions-and-order-copies.md) and explore the flowchart that illustrates how the order subscription item resource relates to the other API entities.

</details>

<details>

<summary>How-to</summary>

Check the related [guide](/how-tos/placing-orders/subscriptions.md) to learn more about how to generate and automatic subscriptions from a source order and how to add, remove, or update order subscription items belonging to an already generated order subscription.

</details>


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