what does this stamp inside ring mean?

[asscherisme]

I have an 18K white gold ring and inside the ring it is stamped 18K and right next to the 18K it is stamped 750. So they are right next to each other like:

18K 750

I know the 18K, but what is 750? Its a ring I got last fall and I have never seen 750 inside a ring before. But I usually go with platinum so 18K is new to me.

 

[jet2ks]

18k is the US hallmark (and I believe UK), 750 is the European one (750=75% gold) They probably put both stamps in all the rings for ease of sales to various countries.