Trying to I.D. my rear vented rotors, need help please Options

[dion9146]

I'm getting some pulsating coming from my rear vented rotors, and the thickness is right at 19mm, so I might as well replace them. I measured the runout this weekend, and it is coming in at .015" - that's a small number but it's still causing pulsating under braking once the brakes get heated up. Plus, I can hear the occassional squeek coming from the rears under braking in a pulsating sound. So again, I'm replacing the rotors.

My struggle comes with identifying what kind of rotors these are off of. I removed one of them this weekend and could not find a part number anywhere. The measure in at 285mm diameter (11.25 inches) with a current thickness of 19mm. That tells me they probably started life as 20mm. I also believe my rear calipers are M's.

So, I either have 69-73 vented rears or 74-77 / 78-83 vented rears, but I don't know if there are diameter differences between these options. Can someone help me figure out what I have so I can order new ones?

Thanks,

Dion