the guy I bought my rims off of said he didn't use hub adapters on his Toyota...should I use them on my cavy?
Konig 
17x7 
40 mm offset
 
Without a doubt, yes.  
30 seconds (if that) of your time and maybe a few bucks (got mine for free) trumps the possibility your wheel falling off on the road.
 
 
Oh, and by "hub adapters" I'm assuming you are using slang for "hub-centric rings."
 
 
yeah hub-centric rings....that's right.  I saw some on e-bay for cheap
thanks