Re: Spacers
"is the ridge part of the cap? If I remove the cap will that cause problems with dust getting into the hub?"
Yes, you do not want to drive with the cap off. I was trying to visualise what might be causing your problem. You have a bunch of black paint and some rust that needs to be cleaned off. If the spacer still doesn't fit up tight then do as AMX has said and get the spacer opened slightly to fit your hub. That
"lip" is suppose to be there and that should be the 66.56 measurement. Most hub and rim manufactures round that out to 66.6 just for the problem you are experiencing. If after cleaning the area the spacer still doesn't fit just open up the spacer a little.
I just measured two old OEM rotors I have taken from my car and they measure on my caliper 66.7mm. So you see there is plenty of "tolerance" allowed from that 66.56 specification.