If the bolt is undone enough that the head clears the cap, saw off the head. If not, drill out the bolt and then remove the cap.
Then either go at the shaft of the bolt with mole grips or something to wrench the star nut out or just drill the shit out of it until you can pick it out.
If the bolt is undone enough that the head clears the cap, saw off the head. If not, drill out the bolt and then remove the cap.
Then either go at the shaft of the bolt with mole grips or something to wrench the star nut out or just drill the shit out of it until you can pick it out.