if theres a little bit of thread sticking out, snap on do a stud remover kit, they are like sockets but have a reverse flute in them, i havnt had on stud that they don remove.
if theres no stud sticking out, snap-on do another kit which contains reverse twist drill bits and reverse twist taps for winding them out.
boths kitts are not cheap but they are the ebst thing ive bought, especialy if you own a landy.