I spoke with a vendor (not one of the site's sponsors) and he indicated that a 10 mm spacer on the 350Z was a real pain. Apparently, the existing hub is about 10 mm. Thus, this size spacer prevents you from centering wheel using the original hub. Further complicating things is that the 10 mm spacer is apparently too thin to add a hub centric ring?

Ichiba makes a 10 mm spacer, but H&R and Eibach do not (supposidly because of the above problem).

Has anyone used a 10 mm spacer?

 

Well (I am sure people love this), I think I answered my own question. Apparently the 10 mm Ichiba spacers have a ring machined in....

http://www.ichibausa.com/350z03.html

Not sure why H&R and Eibach can't do this.....