Center objects

[Abelbus]

Is there a way to center all the objects in a common center?
I cannot center all the objects in the same center and the symmetry is not working well for me. Centering it by hand is not very accurate …

[knacki]

Enter 0 on xyz axis in Gizmo menu.

[Abelbus]

Many thanks!!
I have already solved it, putting all the “X” of my objects to 0.
I was trying to make a symmetrical helmet and I was centering it by hand … I was going crazy