Thank you Peter for your quick reply.
I used the post field. It's sad that I can't combine the item number, which I only enter once, with the usage types that are in the cloneable field group. That way, I could have entered the data only once for the small part and then displayed it for the finished element. This is only possible with the clonable fields for usage. Unfortunately, I can't call up the item number of the small part in combination with the clonable field for the finished element. I would have liked to automate that. I'll just keep trying. Thank you very much.