More than 3mm would require longer studs. The factory studs were engineered for a specific wheel hub thickness. Common spacers are supposed to be used only for caliper clearance where there is a 1mm-3mm clearance issue for a particularly tight spoke design. They were never intended to change the track of the wheel base. This should be done by selecting a wheel with the desired offset. The nut needs a minimum number of threads to hold the proper torque. Too few threads and you're asking for trouble.
This may help.
http://www.ft86club.com/forums/showt...hlight=spacers