In some examples, a method for at least one of preparation or machining of a femoral head formed on a neck of a femur includes selecting an instrument including probing forceps and a guide element including a centering axis. The guide element is coupled to the probing forceps at first and second coupling points disposed along the centering axis such that the centering axis is disposed in a central plane of the probing forceps independent of an opening angle of the probing forceps. The probing forceps are closed with probing jaws symmetrically contacting the neck of the femur at opposite sides with respect to an axis of the neck of the femur. The guide element self-adjusts with closing of the probing forceps so that the centering axis is automatically aligned in the middle with respect to the two oppositely disposed sides of the neck of the femur.
