This is not a Swedish gold hallmark, but is often misidentified as such (my opinion). The Swedish three crowns mark should be in a trefoil cartouche, such that it resembles a cat's paw (and is colloquially nicknamed as such).
I'm pretty sure the ring is by Ostby & Barton (founded 1879 in Providence, Rhode Island). Ostby chose the three crowns trademark in memory of his Scandinavian heritage (he was Norwegian, but Sweden and Norway were a personal union of two kingdoms until peaceful separation in 1905). Ostby went down with the Titanic in 1912 but the company continued production until the 1950s. The later pieces have the initials 'OB' in a cartouche alongside the crowns but it seems that the earlier pieces often did not. That may not be a hard and fast rule. I would also be pretty sure that this is not solid gold, but gold fill with a 14K shell (and likely before the US Silver & Gold Stamping Act of 1906).