1986 Ignition trouble

After replacing the key lock cylinder and the ignition switch, I'm still having problems with the ignition on my '86 mustang lx. When I turn the key, it feels like the berrings (or whatever the key lock cylinder inserts into) is stripped. What is the name of the part that could be causing this problem, or does anyone have any suggestions on what might be causing this problem. Any replys will help. Thanks!!!!!!!