check out this page on my old thread, if it is the same bar they are talking about, it is a 7/8 socket and breaker bar, good luck http://mmb.maverick.to/showthread.php?s=&threadid=4089&perpage=20&pagenumber=1
7/8 ths is correct...just installed one today...had to use a half inch drive socket and a persuader bar to get it off the donor car
The bolt actually has a tapered shoulder on it. I guess this helps pull the frame in slightly if its a little off and keeps things from shifting under extreme loads. Theoretically, of course.