So I got 1st, 2nd, 3rd and 4th synchro installed, 5th and 6th (which are the same part no.) didn't fit, there was like 2mm difference in internal diameter and when I looked closely, they have a small difference in shape and the inside materials are different, I emailed Joe@zspeed to see if he knows anything about that, also I found a different part no. online which is 32604-CD105 but the photo in Z1 shows the same one as I got.
Up old, down new
outside new inside old
