You can have multiple invoice item categories. These categories will allow you to view different groups of invoices, e.g you can view all invoices for parts separately if you need to.
In order to set up an invoice item category, first, go to your system settings. From the 'lnvoicing' section, click 'Invoice item categories'.
You will see a form on the left-hand side and a list of existing invoice item categories on the right-hand side. You can add your new category on the left and it will appear on the right when you click 'Add invoice item category'.