What is the difference between the M3 and the M3X?
The M-Series (including the M3 and M6) are water resistant, dust resistant, and have a peak output of 90 lumens. The X-Series (including the M3X and M6X) are built to military standards and are waterproof (to 66 feet) and dust proof. They have a peak output of 125 lumens and offer greater durability under harsh conditions.