What does 750 Gold 1-AR UNO-AR mean?

750/1000 = 750 means it's 18k gold / 1000 would be 24k

UNO-AR is for the designer = Uno A Erre a very well known Jeweler in Italy.

24k - 1000

20k - 875

18k - 750

16k - 625

14k - 500

12k - 475

10k - 350