Space diagonal
![AC' (shown in blue) is a space diagonal while AC (shown in red) is a face diagonal](/Images/godic/202501/01/Cube_diagonals.svg0654.png")
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In geometry a space diagonal (or interior diagonal or body diagonal) of a polyhedron is a line connecting two vertices that are not on the same face. Space diagonals contrast with face diagonals, which connect vertices on the same face (but not on the same edge) as each other.