i have a 74 260z and the lower alternator bolt came loose while i was driving and took leave of my car so i need to know what size is it so i can get a replacement!!!!.

If it is like a 240z, which I suspect that it is, it takes an M8 X 1.25 bolt. The bracket has a blind hole 32mm deep, so somthing in the 40 - 45 mm length range should work.

no the one on the bottom the long one that the alt pivots by.

no the one on the bottom the long one that the alt pivots by.

I am almost positive that on my 72 240Z there are 2 bolts at the bottom (where the alt pivots). The hole DOES NOT go all the way through the Alternator mounting bracket. You use 2 bolts, one from the front and another from the rear to secure the Alt to the bracket. I don't remember the length of the bolts, but 8mm X 1.25 is correct.

well the one on mine does it had one long bolt that went all the way

can't help you then.