Ecessary for weapons (Borderlands 3)

Several times already had such a thing as accessories for weapons. Attack is already a hell, and what to do with them and how to hang them on the trunks do not understand. It says that in the inventory menu, but there is nothing such is not present. As these accessories to use?
Maybe I'm just blind and can't see? The only thing I can do to configure trunks to repaint them.