While the Conveyor Belt Filter can filter items by category, the Advanced Conveyor Filter allows for specific items to be filtered. Select the item in your hotbar and press "E" while looking at the Advanced Conveyor Filter to set the filter to allow only that item. You can press "T" to invert the filter to exclude the specific item.
If you want to filter specific items out of a mix, place a row of Advanced Conveyor Filters with Hoppers in between. Every Hopper needs a second Filter going to one side. Now, set the Filter that is going to the side to the specific item that shall be taken out of the line. The Filter going to the next Hopper in the line must be set to exclude that item.
Just a line of Hoppers and Filters does not work as intended. The Filter will only filter every second or third item out of that line. This makes it necessary to add another filter that holds the items back for some time.