Cost database: my custom items
When your firm has the product library switched on, My custom items holds the rates you own: what the library does not contain, with your own prices.
Open My custom items. It is the Items workspace restricted to the items your firm created, so you can add, edit and archive them without the library's rows in the way.
Use it for things the merchant does not sell. Labour and plant rates are kept in their own tabs and are not affected.
Overriding or hiding a library product still works, from the Items tab.
Examples
A specialist lintel
The library has no precast lintel in your spec. Add it here with your own unit and rate, then link it to an estimate line like any other item.