Hi Rick,
No, I have always used this option, without a problem - " If vmul is given as negative, then abs(vmul) is the minimum number of voxels to keep ".
I have also run 3dmerge with the -1clust_order rmm vmul option - still get the same result - no clusters found.
3dmerge -prefix XXX -1thresh 2.879 -1clust_order 5 594 Trait_FC_T_Test_FSeed_Nacc_stats_pi_final_Z+tlrc.
Program 3dmerge
++ 3dmerge: AFNI version=AFNI_2008_07_18_1710 (Jul 24 2008) [32-bit]
3dmerge: edit and combine 3D datasets, by RW Cox
++ default -1dindex = 0
++ default -1tindex = 1
++ editing input dataset in memory (1.3 MB)
*** NO CLUSTERS FOUND ***
.