take off your rim
see that circular nub sticking out in the middle of all the studs?
that's supposed to support the weight of the car NOT the studs.

look at your rim
see the hole in the middle? (NOT the holes for the studs)
that hole should fit perfectly and snugly around that nub sticking out on the hub.
if it doesn't you need a little ring thingy to fill up the space.

yes your wheel will stay on without it but all the weight of the car will be support by the studs. not good. our cars aren't supposed to do that.

to clarify these are COMPLETELY different from wheel spacers.
hubcentric spacers DO NOT affect how far out the wheels are.

-marc