I am trying to use 3dclustsim in AFNI to determine the minimum number of voxel in a cluster to reach significance, my understanding is that in the command line the -fwhm s flag refers to the gaussian filter width and NOT the Gaussian Kernel, can anyone point me to how I might be able to obtain this for each hemisphere in freesurfer? I am using my own average brain that I created, but it would help to know how to do this for the fsaverage as well.