Thanks, my 3/4 must be real worn out or something, but I did read metric sizes are slighty different size so I'll try a 19mm.

 

I did not see that anywhere. On the 'smoothie mooncap' page:
http://hubcapmike.com/bhc01-16.html

he clearly states that they WILL fit 2011 HHR wheels. Only later in an email did he tell me:

"These will go on your wheels with no problems if you have the correct steel wheels. Do you have the wheels with the round holes or the 5 spoke steel wheel. They will only fit the steel wheels with the round holes."

Me: Thats it, I have the 5 spoke steel wheels but have already sent these back, they should be there this week. I am disappointed that there was no disclaimer about this... Also, as I understand, as a business you get a shipping discount so it surprised me when my return shipping only cost 22 bucks when I paid about twice that much to receive them.