Chevrolet 2006 HHR Owner's Manual page 328

CAUTION:
{
Rust or dirt on the wheel, or on the parts to
which it is fastened, can make the wheel nuts
become loose after a time. The wheel could
come off and cause an accident. When you
change a wheel, remove any rust or dirt from
the places where the wheel attaches to the
vehicle. In an emergency, you can use a cloth
or a paper towel to do this; but be sure to
use a scraper or wire brush later, if needed,
to get all the rust or dirt off.
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7. Place the compact spare tire on the wheel-mounting
surface.
6. Remove any rust or dirt
from the wheel bolts,
mounting surfaces
and spare wheel.