The FM66 fits flashlights and WeaponLights with 1.47" diameter bezels (front part of the head). It produces a smooth beam of blue light that causes less degradation of night vision than white light. Hunters use the blue filter to track wounded game at night because blood stands out more distinctly against foliage when viewed under blue light. The filter is also useful for close range, non-tactical applications - such as map reading — as it reduces light output intensity. Applying thumb pressure to the FM66's locking tab releases the cover; a spring mechanism keeps the open cover out of the way by holding it flat against the flashlight. A cam-locking lever keeps the entire unit securely attached to the flashlight.
