I will try to answer your question on the trariff duties you will pay when importing sunglasses from UK or Italy, based on the search I did on the US National Trade Commission's website (Link hidden: Login to view) with the help of the guide in our education section - Importing into the US: Papers, Procedures, Duties.
A specific rate is a specified amount per unit of weight or other quantity. This is the type of duty being charged for sunglasses. The percentage of the charge may be affected by the Harmonized Tariff Schedule - So for every dozen of sunglasses you import you will be charged 2.5% if the country of origin is not part of the 'most favored nations' list.
However, no duties will be required if the country of origin is one of the following: Australia, Bahrain, Canada, Chile, Caribbean Basin, Israel, Andean Nations, Jordan, Morroco, Mexico, Oman, Dominic Republic, Peru, Singapore).
A charge of 40% applies to sunglasses imported from countries included in section 401 of the Tariff Classification Act of 1962.
I'm not sure if I'm making sense but I hope I am :) I suggest reading through the 'Importing into the US: Papers, Procedures, Duties' and you'll be able understand and learn more about the entire process. To have a read please go to:
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I do hope this helps!