bummer
I presume you mean the bolt that goes through the centre of flange and into the box?
it threads into the centre of the diff, one each side
passenger side has quite a strong spring holding the flange away from the box, I found i had to use a big lever to move the flange in towards the box before the threads would bite, drivers side, with the xfer box, not so sure
either way, i would strip out the flange (or xfer box) and try and clean up the thread in the diff with a tap, not easy because its quite deep in the box
good luck