Please Help: SF 1 Cell Heads Won't Work on Nitecore Extreme Body!?

Just got my Extreme yesterday. Let me say that the extreme head works well on it's own body, my SF Backup body, or on the VG 1 cell body. However, when I try to put my KL1 or KL4 heads (older), or my SF backup head on the Extreme body, threading goes good, but then gets very stiff. I believe I'm making battery contact though I do not want to fully tighten the head. Does not appear to be crossthreaded, and I did not yet crank down on the O-ring.

Any ideas why my SF heads which run well on other 1 cell bods won't light up on the Extreme bod?

Thanks....Jeff.

Can anybody with the Extreme and SF heads tell me if theirs fits on the Extreme body. I tried again, and all my SF heads will not thread very far onto Extreme before the threading locks. Before even reaching the O-ring. Anybody?

My Extreme body and SF KL4 head work, if you tighten the head all the way, it tight at first but keep tighten it until turn on, after that it easy.