firstly they are nuts and most likely the studs are snapped, trust me if u have the time and money you should do what i done, i removed the exhaust manifold, i got it sandblasted and i got the face machined, more than likelt it will be slightly warped, i then sprayed it with exhaust manifold paint and i replaced every stud while it was off and i got a new gasket and put it all back together and it looks brand new, and its good to know that everything was done properly with new studs and nuts ..