Teammates that keep each other's privates warm apparently win Olympic medals together ... 'cause Tom Daley revealed he once gifted his diving partner, Noah Williams, a "c*** sock" before they nabbed silver in Paris on Monday.
Daley actually told his fans about the unique gift way back in January -- some six months before the two teamed up to podium at the men's synchronized 10-meter diving event in France.
The guys were doing a Q and A on YouTube when Daley said the present was a last-minute 21st birthday gift for Williams.
"We were in the middle of Budapest," Daley said, "and I was like, 'What am I going to get him for his birthday? You know what, I've got yarn, I've got a crochet hook, and I'm going to make him a c*** sock.'"
Williams told their followers that he appreciated the X-rated present -- even revealing he donned it for some of his subscribers on his OnlyFans page.
As for how 30-year-old Daley -- who knits in his spare time -- knew what size to make the gift ... he said that was simple, "I go by the one-size-fits-most rule."
Daley said his diving future is still up in the air after Monday's competition ... but if he does go for gold in the Los Angeles Olympics with Williams, the diver better gear up for four more years of some risqué B-day gifts.