This all came from a Press conference given buy the Japanese Investigstion team and reported on NHK with photos of the bolt penetrating the tank skin taken from within the tank. The size of the rupture was as stated and it appeared not to be the head of the bolt that penetrated, rather the opposite end.
The photo showed a oval tear-like rupture with space around the bolt that the fuel could have flowed through. I did not catch if they specified the size of the bolt as yet.
It will take a few hours for the translations from Japanese to make their way into English media.
The International Herald Tribune already has a brief report confirming this and here is one paragraph confirming my previous "rumour",
Kazushige Daiki, chief investigator at Japan's Aircraft and Railway Accidents Investigation Commission, told reporters Thursday that officials found a bolt, which is on the right wing slat, piercing through the fuel tank. The hole was about 2-3 centimeters (0.8-1.2 inches) in diameter.