First, note that a cluster of 5 cells consists of 4 overlapping pairs of face-bonded tetrahedra (triangular dipyramids) whose long diameter is a 24-cell edge (a hexagon edge) of length . Six more triangular dipyramids fit into the concavities on the surface of the cluster of 5, so the exterior chords connecting its 4 apical vertices are also 24-cell edges of length . They form a tetrahedron of edge length , which is the second section of the 600-cell beginning with a cell. There are 600 of these tetrahedral sections in the 600-cell.