handbook says:
"Installing the spare tire
The spare tire is designed for emergency
use. See specific instructions under the
heading “Wheels and tires†in the “8. Maintenance
and do-it-yourself†section.
1. Clean any mud or dirt from the surface
between the wheel and hub.
2. Carefully put the wheel on and tighten the
wheel nuts finger tight. When replacing a
front tire, make sure the hole in the spare tire
wheel is aligned with the pin on the brake
rotor"
The 'pin' (small bolt with metal sleeve) is pretty useless really and can be left off. However the thread it screws into provides a useful means of separating the disc from the hub when they need changing, by winding in a bolt