Designed for 3/8-32 LED module for E-Tac Light. Also works for bow sight lights with 3/8-32 thread. CNC T6 Aluminum, high quality anodizing. To connect a fiber directly to the LED, you will need a fiber adapter, which works with a 3/8-32 LED. To fix the fiber, put the fiber through the silicone tube, put the silicone tube into the adapter. Option 1: push the tiny rubber piece into the tube, and put the heat shrink tube on top and shrink it. The heat shrink tube will apply just a little pressure to keep the fiber in the tube. Option 2: Use the rubber ring to apply pressure on the silicone tube. Our fiber adapter is one-piece CNC aluminum, no more plastic rings. It works well with our new 3/8-32 LEDs now featuring an optical convex lens.