It is most likely the maker's initials.
NB or N&B could stand forNeustadt & Barnett, who were ring-makers from Birmingham in the UK in 1839.
If there is an SN somewherearoundthe NB, it was made byN B & Sn in 1941, London, UK.
It could also be theNayler Brothers (1926-1988).
Or maybe Needham Brothers (1901-1917).
The best way to get a proper definition of the NB is to ask aprofessionaljeweller.
Nb is the chemical symbol of niobium.
Note well (NB is latin!)
NB stands for Nominal Bore.
nominal bore
Niobium
Nickel Back
I am not quite sure what you mean by "nb", but I don't think it's a unit of length.
nb nb kj:)
I suspect that NB stands for the Latin phrase nota bene,whick means 'note well'.
You can clean your ring with steam, or warm, soapy water. NB: Close the sink drain, and cover it with a cloth, so that if you drop the ring, you won't lose it to the drain.
NOTA bENE
What does zet mean on a ring