afni.nimh.nih.gov

You should choose a cluster table depending on
the desired neighbors and sidedness of the test.
That table would give you a minimum cluster size,
based on the uncorrected and corrected p-values
you are using.

Then that cluster size is applied to the 3dttest++
statistical output (either in the afni GUI or in a
3dclust or 3dClusterize command).

- rick