"how much of the infinity clip do you cut off and what tool did you use to do it? I just got my Fenix today".
You don't have to cut anything off the clip if you like it as-is. I wanted to get the clip closer to the end of the flashlight, so I cut off the "ears". (That is Grubbster's term, and it works). Just look at the clip and see the two pieces of metal that extend above the rest. Harder to explain than to see. Cut off all, some or none, to get the clip in the proper position for your use.
I used a dremel tool with a cutoff wheel. I put a piece of masking tape along the cutoff line as a reference. I changed to a dremel sanding drum to pretty things up after the cut was finished. This leaves some shiny silver metal on the edge where the cut is made. I used "oxpho-blue", a cold bluing solution, on a q-tip to touch up the cut and make it black again. Oxpho-blue (available at Brownell's) is arguably the most durable cold blue, but you can get a basic blue touch up pen at any decent sporting goods store that sells firearms. The standard cold blue solutions don't hold up all that well, but the location of the touch up shouldn't get much wear anyway.
Hope that helps, TR