The Atlas · Gold fineness mark
375 means 9 karat gold: 375 parts gold in every thousand, 37.5% gold by weight. It is a British standard alloy and it is genuinely gold — just a little over a third of it, which is why so much of it turns up in an estate box and disappoints.
What does 375 mean on a gold ring? — answered here in full, free, with nothing asked of you.
Nine carat was made legal in Britain in 1854 and became the working-class wedding band, the confirmation cross, the charm bracelet and the signet ring of the entire twentieth century. If a box came out of a British household, most of the gold in it will be 375. American families find it in boxes brought over by a parent or grandparent, or bought on a trip.
Americans routinely conclude 375 must be fake, because the United States does not permit a 9 karat alloy to be sold as gold at all — the federal minimum is 10 karat. It is not fake. It is a legal British gold alloy with a lower gold fraction, and a refiner will pay for it accordingly: roughly 37.5% of the piece's weight, priced at the day's gold spot, less the refiner's margin.
Because the alloy is nearly two-thirds copper and silver, 9 carat wears differently. It holds a crisp edge on an engraved signet longer than 18 carat does, and it tarnishes and pinks with age in a way that reads as old but proves nothing about the date. British 375 pieces frequently carry a full hallmark row, and on those the date letter will give you the year outright — which is the single most useful thing in the box.
The stamp is present and legible: this metal is declared 9 karat gold, 375 parts per thousand.
British or Commonwealth manufacture, after 1854. If an anchor, a leopard's head, a castle or a rose sits beside it, the piece was assayed by a named office and a date letter in that same row will date it to a single year.
The weight, and therefore the melt value; whether a hollow chain or a tube bangle is as heavy as it looks; and whether a repair or a fitting elsewhere on the piece is a different metal entirely.
Next step
If there is a row of small punches beside the 375, photograph the whole row in one frame rather than the numbers alone. The shape of each shield and the font of the date letter are what fix the year, and they only read as a set.
8 karat, 375's German cousin. A third gold, and the lowest alloy called gold anywhere in Europe.
10 karat, the American minimum. Close in feel to 9 carat and worth about 11% more per gram.
Not solid. A 9 carat layer bonded over brass, common on Victorian and Edwardian chains and lockets, with scrap value close to nothing.
A rubbed 375 and a rubbed 875 or 975 are easy to confuse under bad light, and neither of those is a gold standard at all.
Free, and nothing asked of you
One mark answers one question. A box answers the real one — which pieces deserve money and expertise, and which nine are costume. Email the photographs to the house inbox: the whole box laid out, then any stamps you can find. We read them and reply by hand.