clusters.out

Dear all
4
6.510000
2
0.500000 0.500000 0.500000 1 1
-0.500000 -0.500000 -0.500000 1 1
this is the clusters.out file line.
What is the meaning of 1 1 after atomic positions.
This output is for TiVZr_bcc system. Can we say which pair is considered here by looking at 1 1 in both the lines .