I love this stunning Finnish 1960s space-age ring. It has certainly been made with great skill and craftsmanship. It has the maker's mark inside the hoop next to the 925 mark. This mark is for the designer Elis Kauppi and is for his Kupittaan Kulta firm.
Elis Kauppi (1924-2001) started his own firm, Kupittaan Kulta, when he was only 24 years old. His sophisticated, modernist designs often include semi-precious stones, some of which can be found in Finland.
My ring dates to 1965. It has a thick hoop and the decoration on the front is a circular band with a pointed cone shape inside.
It is marked inside the hoop 925 and with a letter O in a square. This is the maker's mark, as photographed.
It is a nice larger size and will fit a UK finger size N/O (it is probably nearer to being a Size O). I have photographed it for your inspection on a ring sizer.