Not really, it's the outer diameter that goes into the wheel. Your spacers should be 57.1 on the inner diameter to sit on cars hub and normally it will be 57.1 on the outer diameter to fit in the wheel, I've never seen spacers that convert hub sizes before. If your wheels are 73.1 then you'll need 73.1 to 57.1 spigots and spacers will be 57.1 so I'm lost as to where you're getting the 66.6 from?