I created a Custom Module that I'm calling "Item Purchasing Group".

This module will store information for groups of Items that must be purchased together (including minimum overall quantities and/or values, etc.).

This will have a one-to-many relationship with individual Items.

Unfortunately, when I go to add a Custom Field to the Items (a Lookup type to point at the Custom Module), the Custom Module isn't available.

Am I missing something, or is this the expected behavior?