Usain Bolt teamed up with Hublot to make the custom see-through timepiece -- we're told it's worth around $50,000 -- and they're auctioning it off to fight muscular dystrophy.

It's call the "Big Bang Unico Sapphire" -- and features sapphire, 18k gold and a silhouette of Bolt's signature pose on the the dial!!

It's 1 of 1 -- the only Bolt special edition ever made -- and it's part of the Only Watch charity auction with the winning bid going to medical research to fight muscular dystrophy.

There's more ... the auction winner also gets a meet and greet with Bolt himself.

FYI, bidding goes til November if you wanna throw down.