Mount caster/camber gauge

I know this is a long shot but has anyone used one of the caster/camber gauges with Cragar SS wheels? Before I pull the trigger and buy one I was wondering if the magentic adapter they come with fits in the center hole and sticks on the grease cap.... They don't tell you the diameter of the magnetic adapter so its a bit of guess work.
I have a magnetic caster/camber gauge, and I use my spare tire/wheel and another spare from a junkyard (both with steel rims and same size tires) to set the alignment. After the alignment is set, put the mags back on and you are ready to roll.