Same problem to me.
I got these great 18" saleen wheels from ebay and the lugs they've send i gues are not exactly matching. therefore i've had some siezed and not be able to take them out.
Now i have to brake the studs. I complaint to the company i bought the wheels from, but all they did is just some new lug nuts which are exactly the same. They said they've never had this problem before and they sell wheels for stangs everyday. Whatever.
Now i just have an extra set of lug nuts and locks, saying to be 1/2-20. I still don't know if they are the right ones. I anyone knows the the size of threads it should be i would appreciate.