White had the belt custom made for this fight after Nate said the bout would determine the real baddest mofo in combat sports.
Dana says the belt cost around $50,000 to make -- and it's engraved with the words, "Baddest Motherf**ker."
White has previously said the belt is a one-time thing for this specific fight -- but there are a bunch of fighters who have said they'd love to get a crack at it ... so we may not see the last of it after Saturday.
As far as the fight goes, Diaz is the #7 ranked welterweight and Masvidal is #3. The current champ in that division is Kamaru Usman.