You will never find two venders with the exact same parts for CE4,CE5, CE6, and Vivi Novas, even the ones that claim genuine Vision parts and even ones that have the logo etched on the product. You will waste time and get frustrated if you don't always order parts and replacement heads from the same place. It sucks, but what can we do about it?
There will always be slight differences, usually height of post or head.