ASK 97-YEAR-OLD ISADORE ROSENTHAL his secret to long life, and he'll tell you there is none: "I just eat plain food." But ask him how he got lucky enough to celebrate a 75th wedding anniversary this month with his wife, Sarah, 93, and there's no hesitation. "I'm not lucky," says the sprightly nonagenarian. "I'm blessed."

And so, it seems, is the simple gold band that he slipped onto his bride's finger on their wedding day, Nov. 5, 1922. Since then the ring, originally his mother's, has been loaned out for the nuptials of 15 relatives—children, grandchildren, nieces and nephews—with impressive results. Not one of the marriages has ended in divorce.

The Rosenthals met in Washington in 1918, when Isadore was 18 and Sarah Seigel only 14. Three years later, Isadore proposed on bended knee. Over the years he worked as a Navy engineer and a real estate manager, while Sarah was a homemaker. Their two children—Bette, 73, who recently celebrated her 50th anniversary, and Helen, 68, who is coming up on her 49th—agree that their parents' devotion to each other, not the ring, inspired the family's uninterrupted reign of matrimonial harmony.

Yet the Rosenthals' 14 great-grandchildren look forward, as their parents did, to using that ring. "It'll be passed down from generation to generation," says Bette's husband, David Gordin, 76, "because they know the kind of lives these two people have led, and they hope to have the same."