O, A, and B disk????

Ok I have done a search and the info I read was very helpful but still a little unsure.... 

So that brings me to this, I read that O, A, and B disk is superlow, high, and low disk... Now it mention something about the brake calibers "sorry I suck at spelling" size to figure the disk that is needed for the car. So I am guessing that if someone is running a large brake kit they would need "A" high disk unless they sink in right??? 

and as for "O" superlow would be like some tiny rear brakes or drums right? I don't know if I understand or if I'm on the right track. So can someone point me in the right direction.... 

And how do I know what disk I need from "O, A, and B"???

I mean I am trying to learn thi so I can buy the right wheels for my 300ZX and I know... it's not a VIP car but it would help me set the opions for my wheels on my wide-body sentra....

Yeah you're on the right track with that.
Just measure how far you need the back of the spokes from the hub in order to clear your calipers.
You can run superlow on stock econocar discs or drums usually

If you have a z32 youll need R disk front and O disk rear. O, A and R is designations used primarily by Work wheels. So, for another brand like AME they use super low, low and high. SSR is super low, medium and high disk. Anyway, for your Z youll need whatever one is for big brakes(high disk, or R) and whatever is the lowest for the rear I believe(super low, or O)

Ok... I guess I'm doing well. I am looking at a set of SSR wheels... Witch I can use on both my Sentra or 300ZX right now. But I didn't qite understand the disk issue and was afrad that I was going to have major issues after investing a large amount of money on something I wasn't going to be able to use. But I am working on a widebody on both cars.... So Thanks for the help!